GNITION 


CarlA.PfanstiJW 


AU.  j 

GIFT  OF 

^••"/ 

I G  N  IT  I O  N 

BY 

CARL  A.  PFANSTIEHL 

President  Pfanstiehl  Electrical  Laboratory 


SECOND  EDITION 


With  Original  Diagrams 
and  Photographs 


$1.00 


Penton  Publishing  Co 
Cleveland,  O 


Copyright  1912 

by 

The  Penton  Publishing  Co 
All  rights  reserved 


GJ0  tlf*  mrmurit  of 

iflntltrr 


464513 


IGNITION 


CARL    A.    PFANSTIEHL 


Introductory 

Before  entering  upon  the  study  of  electric  ignition,  it 
will  be  well  to  mention  a  few  facts  concerning  electricity 
itself.  What  is  this  wonderful  agent  which  can  be  sent 
through  a  small  wire  many  miles  long,  then  made  to  run 
our  heaviest  machinery  or  to  do  almost  anything  from 
carrying  the  delicate  vibrations  of  the  human  voice  from  one 
city  to  another,  to  the  more  difficult  task  of  rendering  visible 
to  the  physician  the  broken  bones  of  his  patient,  and  last, 
but  by  no  means  least,  to  enter  the  cylinders  of  our  engines 
and  ignite  the  charge  at  the  proper  instant?  To  this,  science 
as  yet  has  no  definite  answer.  However,  enough  is  known 
regarding  its  action  to  enable  it  to  be  handled  with  at  least 
some  degree  of  certainty. 

There  are  two  principal  forms  of  electricity :  Elec- 
tricity at  rest,  known  as  "Static  Electricity''  and  electricity 
in  motion,  or  "Current  Electricity!'  Matter  may  be  divided 
into  two  classes  with  respect  to  electricity — insulators 
through  which  it  cannot  pass,  and,  therefore,  must  remain 
where  it  is  placed,  and  conductors  through  which  it  can  pass 
or  flow. 

Static  electricity  can  be  produced  by  friction;  for  in- 
stance, by  rubbing  some  good  insulator,  such  as  a  glass  or 
hard  rubber  rod,  with  a  piece  of  dry  silk  or  woolen  cloth. 
Its  presence  on  the  rod  can  be  shown  by  the  latter's  power 
of  attracting  small  bits  of  paper,  wood,  etc.  It  is  easy  to 
show  that  this  electricity  is  static,  by  rubbing  only  a  part  of 

1 


Ignition 

the  rod  with  a  cloth  and  observing  that  the  power  of  attract- 
ing the  paper  is  found  only  on  that  part  of  the  rod  which 
is  actually  rubbed.  If  a  conductor,  such  as  a  brass  rod,  is 
held  in  the  hand  and  rubbed  with  a  cloth,  it  exhibits  no 
such  power  of  attraction.  The  electricity  which  is  thereby 
produced,  passes  from  the  rod  through  the  body,  a  conduc- 
tor, into  the  earth.  It  does  not  remain  static  on  the  rod,  but 
passes  off  as  a  current.  If  the  conducting  rod  is  provided 
with  an  insulating  handle  and  rubbed  as  before,  the  elec- 
tricity so  produced  will  flow  to  all  parts  of  the  rod,  and 
when  it  has  spread  over  the  entire  surface,  it  ceases  to  flow 
and  becomes  static.  Thus  the  entire  rod  possesses  the 
power  of  attraction,  even  though  one  part  only  is  rubbed. 
The  rod  is  now  said  to  be  charged  with  static  electricity. 
We  will  have  occasion  to  refer  again  to  static  electricity 
when  discussing  the  action  of  the  condenser  in  a  jump 
spark  coil. 

Our  concern  here  will  be  mostly  with  the  phenom- 
enon of  electricity  in  motion,  or  current  electricity. 

It  can  be  seen  from  the  above  that,  in  order  to  maintain 
a  current  of  electricity,  it  is  necessary  that  the  part  or  cir- 
cuit, through  which  it  flows,  be  composed  entirely  of  con- 
ductors. If  the  conducting  circuit  is  broken  in  any  place 
and  an  insulator  interposed,  the  flow  of  current  is  thereby 
stopped  and  it  then  remains  static  in  the  circuit.  As  a  mat- 
ter of  fact,  however,  it  does  not  remain  static  very  long 
unless  the  circuit  is  unusually  well  insulated.  It  leaks  out 
and  finds  its  way  to  the  earth,  where  it  is  neutralized. 

The  force  which  tends  to  move  electricity  must  also  be 
present  in  the  circuit  if  the  current  is  to  be  maintained. 
This  is  called  Electro-Motive-Force,  abbreviated,  E.  M.  F. 


Introductory 


Only  the  two  principal  methods  for  producing  the  E. 
M.  F.  will  be  considered,  viz. :  Galvanic  and  Dynamic.  The 
former  is  a  chemical  action,  the  latter  a  mechanical  one, 
consisting  of  a  conductor  being  made  to  pass  across  a  mag- 
netic field.  The  former  method  includes  all  kinds  of  bat- 
teries— the  latter  dynamos  and  magnetos.  We  will  con- 
sider first  the  Galvanic  method,  later  taking  up  the  Dy- 
namic, under  the  head  of  "Dynamic  Electricity". 


Photos   showing  a   cast   lead    grid,    for   a    storage   battery, 
before  and   after   filling  the   pockets   with 
the   active   material. 


Forewoid 


This  book  was  written  in  response  to  a  growing  demand  for  an 
explanation  of  the  fundamental  principles  of  Electric  Ignition. 

The  author  aims  to  show  the  real  simplicity  of  a  subject  too 
generally  considered  obscure,  and  he  believes  that  the  most 
inexperienced  gas  engine  operator,  after  carefully  reading 
these  pages,  will  be  greatly  aided  in  solving  the  mysteries  of 
his  ignition  system. 

Chapter  Fourteen  on  low-tension,  built-in,  gear-driven,  make- 
and-break  magnetos  will  be  found  especially  timely  and 
helpful  to  the  progressive  manufacturers  of  stationary  farm 
engines,  many  of  whom  already  have  adopted  as  standard 
equipment  this  type  of  ignition  in  which  all  batteries  and 
high-speed  friction-driven  generators  are  eliminated  and  the 
entire  ignition  system  made  an  integral  and  permanent  part 
of  the  engine. 

The  writer  presents  with  special  pleasure  the  oscillograph 
tests  made  by  him  in  his  laboratory,  which  show  with  absolute 
accuracy  the  action  of  vibrating  and  make-and-break  coils, 
and  the  current  wave-forms  of  various  magnetos.  These 
original  and  new  experiments  enable  him  to  give  information 
that  will  prove  to  be  of  particular  interest  and  value  to  the 
student  of  ignition. 

The  author  wishes  to  express  his  thanks  to  Mr.  Oscar  Bell, 
who  prepared  the  drawings. 


CONTENTS 

Introductory. 

Chapter  I.  Batteries.  Primary  Batteries — Edison  Pri- 
mary Cell — Gordon  Cell — Dry  Cell — Secondary  or  Storage 
Batteries — Edison  Storage  Battery. 

Chapter  II.  Electrical  Units  and  Laws  Governing 
the  Flow  of  Electricity.  Volt — Ampere — Ampere 
Hour — Ohm — Watt — Ohm's  Law — Series  Connections — 
Parallel  Connections — Joint  Resistance — Current  in 
Branch  Circuits — Resistance  of  Different  Materials — 
Table  of  Comparative  Resistances. 

Chapter  III.  Connecting,  Testing  and  Care  of  Bat- 
teries. Testing  Dry  Cells — E.  M.  F.  of  Cells — Amperage 
of  Cells — Testing  Storage  Batteries — Installing  Batteries — 
Voltage  and  Amperage  of  Set  of  Cells — Current  from  Cells 
in  Multiple — Tests  of  Cells  in  Multiple. 

Chapter  IV.     The  Simplest  Form  of  Electric  Ignition. 

Make  and  Break  Ignition. — Electric  Inertia  and  Momen- 
tum— Magnetic  Field — The  Igniter. 

Chapter  V.  Construction  and  Operation  of  Make  and 
Break  Coils.  Make  and  Break  Coils — General  Form  of 
Igniter — Loss  of  Compression — Igniter  Points — Duration 
of  Spark — Time  Length  of  Contact. 

Chapter  VI.  Oscillograph  and  Tests.  The  Oscillograms 
of  Make  and  Break  Coils — E.  M.  F.  of  Spark— Magnetic 
Plug  System. 

Chapter  VII.  Theory  of  the  Jump  Spark  Coil.  Spark 
Voltage — Theory  of  Jump  Spark  Coil — Theory  of  Con- 
denser— Theory  of  Vibrator — Complete  Action  of  Coil. 

Chapter  VIII.  Practical  Construction  and  Operation 
of  the  Jump  Spark  Coil.  The  Primary — The  Vibrator 
—The  Condenser — Secondary  Winding — Pancake  Wind- 
ing— Balance  of  Parts. 

Chapter  IX.  Oscillograph  Tests.  Non-Vibrating  Jump 
Spark  Coils. 


Contents 


Chapter  X.  Dynamic  Electricity.  How  an  Electric 
Current  is  produced  by  mechanical  Means  in  Dynamos 
and  Magnetos — Magnetism — Magnetic  Strength — Mag- 
netic Density— Collecting  Brushes — Commutator — Mag- 
netic Circuit — Armature — Difference  between  Magnetos 
and  Dynamos — Shunt  Wound — Series  Wound. 

Chapter  XI.  Low-Tension  Dynamos — Direct  and 
Alternating  Current — Low-Tension  Magnetos.  The 

Low-Tension  Dynamo — The  Commutator — The  Direct- 
Current  Magneto — The  Alternating  Current  Magneto— 
The  Inductor  Type  Alternating  Current  Magneto. 

Chapter  XII.  High-Tension  Magnetos— Their  Theory 
and  Construction.  High-Tension  Magnetos — Theory 
of  the  Pure  High-Tension  Magneto. 

Chapter  XIII.  The  Installation  and  Care  of  High- 
Tension  Magnetos.  Timing  the  Magnetos — Care  of 
High-Tension  Magnetos — The  Magnetic  Circuit — Wind- 
ing the  Armature — Collecting  Ring  and  Brush — The 
Condenser — The  Interrupter — High  Tension  Distributor 
— Safety  Spark  Gap. 

Chapter  XIV.  Low  Tension  Positively  Driven  Make- 
and  Break  Magnetos  for  Stationary  Engines. 

Operation  of  System — Construction  of  Magneto — Field 
Magnets — Armature — Grounding  Brush — Collecting  Ring 
and  Brush — Bearings — Current  Waves — Timing  the  Mag- 
neto— Relation  of  Engine  and  Magneto  Speeds — Multiple 
Cylinder  Engines — Wear  of  Igniter  Points — Insulation 
of  Igniter — Heat  of  Arc — Sizes  of  Magnetos — Oscillating 
Make-and-Break  Magnetos. 


Chapter  One 
Batteries 

Batteries  are  divided  into  two  general  classes,  namely, 
Primary  and  Secondary.  In  the  former  the  current  is  pro- 
duced by  a  chemical  decomposition  of  the  active  materials. 
Tn  the  latter  by  a  kind  of  chemical  change  of  the  active  ma- 
terials, which  change  can  be  reversed,  thereby  restoring  the 
elements  to  their  original  state.  \ 


Cross  section  of  ordin- 
ary dry  cell.  Fig.  B 
shows  cross  section 
of  carbon  rod,  which 
has  large  surface  area 
insuring  good  con- 
tact with  the  granu- 
lated carbon. 


Diagrammatic    view    of    a    simple    galvanic 
cell. 


5  ^Lc  H^  c^'  tfc*  ****•  Ignition 

PRIMARY  BATTERIES. 

Primary  batteries  consist  essentially  of  a  chemical  solu- 
tion, called  the  electrolyte,  in  which  are  placed  two  conduc- 
tors, one  of  which  will  be  attacked  more  rapidly  by  the  solu- 
tion than  the  other.  During  this  process  the  element  which 
is  acted  upon  most,  usually  receives  a  negative  charge  of 
electricity,  and  if  a  wire  is  connected  between  the  elements, 
a  current  flows  through  it  from  one  to  the  other.  This  cur- 
rent continues  to  flow  until  either  the  solution  or  one  of  the 
elements  is  exhausted  or  until  the  chemical  action  is  tem- 
porarily checked  by  bubbles  of  hydrogen  gas  which  form 
and  collect  on  the  negative  element,  thereby  insulating  it 
from  the  solution.  In  this  case,  the  wire  connecting  the 
plates  must  be  disconnected  and  the  cell  allowed  to  stand  or 
recuperate  until  the  bubbles  pass  off,  thereby  allowing  the 
chemical  action  to  proceed.  This  process  is  known  as 
"polarization"  and  is  one  of  the  most  important  factors  to 
be  considered  in  the  construction  of  primary  batteries.  It 
is  obvious  then,  that,  if  the  current  is  to  be  maintained,  this 
polarization  must  be  entirely  prevented. 

This  is  accomplished  only  in  certain  types  of  batteries, 
known  as  "closed  circuit."  When  a  current  is  wanted  for 
only  a  few  seconds  at  a  time,  as  in  ignition  apparatus,  where 
the  intervals  of  rest  between  current  impulses  are  compara- 
tively long,  batteries  in  which  the  polarization  is  only  par- 
tially checked,  are  satisfactory  and  somewhat  easier  and 
cheaper  to  make.  These  are  known  as  "open  circuit  bat- 
teries." 

While  there  are  a  great  many  varieties  of  primary  bat- 
teries employing  different  elements  and  solutions,  most  of 
them  are  more  or  less  unsuitable  for  ignition  purposes, 

6 


Batteries 


chiefly  for  mechanical  reasons.  The  solutions  are  easily 
spilled,  the  glass  jars  are  large  and  readily  broken,  and  the 
active  elements  are  more  or  less  expensive  and  troublesome 
to  renew  when  exhausted.  The  internal  resistance  of  these 
types  of  batteries  is  usually  quite  large,  which,  as  we  shall 
see  later,  reduces  the  available  current  output. 

There  are,  however,  two  types  of  liquid  cells,  known  as 
the  Edison  Lalande,  now  called  Edison  Primary,  and  the 
Gordon,  which  have  been  found  to  be  a  satisfactory  source 
of  current  in  isolated  places,  where  there  is  plenty  of  space 
and  no  great  vibration,  and  where  it  is  inconvenient  to  have 
a  storage  battery  recharged. 

It  may  be  well  to  give  a  brief  description  of  these  cells 
which  are  of  the  closed  circuit  type,  and,  therefore,  suitable 
for  electric  lighting  as  well  as  ignition.  The  active  elements 
are  zinc  and  copper  oxide  in  a  solution  of  caustic  potash 
(potassium  or  sodium  hydrate). 

THE  EDISON  PRIMARY  CELL. 

In  the  Edison  Primary  cell  the  copper  oxide  with  some 
magnesic  chloride  added  to  it,  is  molded  under  pressure  into 
plates  of  the  proper  size  and  then  baked ;  the  magnesic  chlor- 
ide serving  to  bind  the  mass  together.  The  black  oxide 
plate  thus  formed  is  suspended  in  a  copper  frame  between 
two  thick  plates  of  zinc.  Polarization  is  done  away  with  in 
this  case,  since  the  hydrogen  as  fast  as  it  forms,  combines 
with  the  oxygen  of  the  copper  oxide,  forming  water,  thus 
gradually  reducing  the  oxide  to  red  metallic  copper.  The 
amount  of  black  active  oxide  left  in  the  plate  at  any  time 
can  be  ascertained  by  picking  into  it  with  a  pen  knife.  If 
the  plate  is  red  throughout  the  entire  mass,  it  is  exhausted 
and  requires  renewal.  If,  however,  there  is  a  layer  of  black 

7 


Ignition 

in  the  interior,  there  is  some  life  left,  the  amount  depending 
upon  the  thickness  of  the  layer  of  black  oxide  still  remain- 
ing. 

It  is  very  important  that  a  layer  of  heavy  paraffine  oil 
about  Y4  inch  thick  be  kept  floating  on  the  surface  of  the 
solution  to  prevent  corrosion  and  to  protect  it  from  a  de- 
teriorating chemical  action  with  the  air.  If  this  is  not  done, 
the  life  of  the  battery  will  be  reduced  over  one-half.  It 
is  also  necessary  to  have  the  oxide  plate  kept  one  inch 
below  the  surface  of  the  solution.  This  cell  gives  an  E.  M.  F. 
of  0.7  volts  and  can  furnish  a  current  continuously  dur- 
ing its  life  of  from  two  to  seven  amperes,  depending,  of 
course,  upon  the  size  of  the  active  elements.  These  cells 
range  in  size  from  150  to  600  ampere-hour  capacity. 

THE  GORDON   CELL. 

In  the  Gordon  type  of  cell,  the  oxide  is  powdered  or 
flaked  and  contained  in  a  perforated  sheet  iron  can.  The 
zinc  takes  the  form  of  a  cylinder  placed  around  the  oxide 
can  and  held  in  place  by  porcelain  lugs.  The  containing  jars 
are  either  porcelain  or  enameled  steel,  and  with  the  latter,  a 
tight  fitting  compressed  fiber  cover  is  used,  which  is  prac- 
tically liquid  tight,  thus  making  the  cell  suitable  for  portable 
engine  and  marine  work.  It  is  extremely  easy  to  renew  the 
exhausted  elements  of  this  cell,  as  the  loosening  of  one 
screw  will  permit  the  exchange  of  both  the  oxide  can  and 
the  remains  of  the  zinc  for  fresh  elements.  A  layer  of 
paraffine  oil  must  be  kept  on  the  surface  of  the  solution  as  in 
the  Edison  Primary  cell.  Both  the  Edison  and  the  Gordon 
batteries  have  the  advantage  of  never  freezing  and  while 
severe  cold  slightly  reduces  their  efficiency,  it  by  no  means 


Batteries 


prevents  their  satisfactory  action.  Gordon  cells  have 
worked  satisfactorily  at  a  temperature  of  15  to  20  degrees 
below  zero. 

THE  DRY  CELL. 

The  most  popular  primary  battery  is  the  well  known 
dry  cell. 

The  active  elements  of  the  dry  cell  are  zinc  and  carbon 
in  an  electrolyte,  consisting  principally  of  ammonium  mur- 
iate. The  containing  can  is  made  of  sheet  zinc,  which  also 
forms  an  efficient  positive  element,  as  the  active  surface  is 
large.  The  inside  of  the  zinc  can  is  lined  with  some  absorb- 
ent material  such  as  blotting  paper,  and  to  prevent  internal 
short  circuit  great  care  must  be  exercised  that  no  cracks  or 
holes  are  left  to  allow  the  zinc  to  come  into  direct  contact 
with  the  carbon.  A  rod  of  solid  carbon  carrying  a  binding 
post,  is  placed  in  the  center  and  the  space  around  it  is  filled 
with  a  solidly  packed  mass  of  granular  carbon,  forming  a 
•negative  element.  With  this  carbon  is  mixed  some  manga- 
nese dioxide  as  a  depolarizer.  The  fibrous  lining  is  satur- 
ated with  a  solution  consisting  principally  of  ammonium 
muriate,  which  forms  the  electrolyte.  The  cell  is  then  her- 
metically sealed  with  some  kind  of  sealing  wax.  In  this 
way  the  elements  present  large  active  surfaces  without  un- 
duly increasing  the  size  of  the  cell. 

When  the  cell  is  put  to  work,  it  starts  to  polarize ;  that 
is,  hydrogen  gas  is  formed  in  quantities  depending  prin- 
cipally upon  the  rate  at  which  the  cell  is  discharged,  and,  un- 
less the  gas  is  absorbed  in  some  way,  it  will  not  only  inter- 
fere with  the  chemical  action,  but  will  cause  the  cell  to  swell 
or  puff  out,  sometimes  even  bursting  it.  If  the  hydrogen  is 
not  formed  too  rapidly,  however,  it  is  disposed  of  by  com- 


Ignition 

bining  with  the  oxygen  of  the  manganese  dioxide  which  was 
mixed  with  the  carbon.  If  the  cell  is  discharged  at  a  rate 
high  enough  to  cause  hydrogen  to  be  produced  more  rapidly 
than  the  manganese  dioxide  can  absorb  it,  the  cell  will  soon 
be  ruined  unless  it  is  given  frequent  intervals  of  rest  long 
enough  to  allow  the  gas  to  be  absorbed.  This  is  how  a  cell 
recuperates.  If,  on  the  other  hand,  the  rate  of  discharge  is 
kept  so  low  that  the  gas  will  be  absorbed  as  fast  as  it  is 
produced,  the  cell  will  not  need  to  recuperate  as  much  and 
can  be  used  on  closed  circuits  such  as  electric  lighting. 
The  closed  circuit  discharge  limit  for  most  good  dry  cells 
is  about  one-quarter  ampere  and  better  results  are  obtained 
with  even  less.  This  is  why  the  life  or  efficiency  of  a  dry 
cell  is  so  dependent  upon  the  rate  of  discharge.  The  greater 
the  discharge  rate,  the  longer  and  more  frequent  must  be 
the  intervals  of  rest,  and  the  less  will  be  the  total  efficiency. 
This  will  be  considered  later  more  in  detail  when  the  meth- 
ods of  caring  for  and  connecting  cells  are  described. 

The  success  of  a  dry  cell  depends  not  only  upon  the 
selection  and  purity  of  the  elements  used  but  upon  the  man- 
ner and  uniformity  with  which  they  are  handled  during  the 
process  of  manufacture.  For  instance,  an  impurity  on  the 
inside  surface  of  the  zinc  will  usually  be  all  that  is  needed 
to  constitute  a  tiny  local  cell,  which  causes  a  current  to  flow 
from  the  impurity  to  the  zinc  and  back  again  through  the 
electrolyte.  This  will  continue  until  the  speck  of  foreign 
matter  is  set  free  by  the  surrounding  zinc  being  eaten  away 
or  until  the  electrolyte  around  it  is  exhausted.  This  process 
is  known  as  "local  action"  and,  fortunately,  in  the  better 
grades  of  dry  cells  is  practically  prevented.  A  careful 
manufacturer  of  dry  cells  uses  machinery  largely  in  the 

10 


Batteries 


work,  thus  eliminating  the  variable  personal  factor,  and  sev- 
eral tests  for  voltage  and  amperage  are  made  during  the 
process  of  construction.  The  cells  are  then  allowed  to  sea- 
son for  four  days  and  after  a  final  test  are  packed  for  ship- 
ment. 

SECONDARY  OR  STORAGE  BATTERIES. 
A  brief  mention  only  can  be  made  of  the  principle  of 
the  secondary  or  storage  battery.  In  this  cell,  as  stated  be- 
fore, the  current  is  the  result  of  a  chemical  change,  which 
takes  place  within  the  cell.  This  change  differs  from  that 
in  the  primary  cell,  in  that,  when  the  active  elements  are 
exhausted,  it  is  not  necessary  to  replace  them  with  new  ones, 
but  the  old  ones  can  be  re-formed  or  reconstructed,  as  it 
were,  by  passing  a  current  of  electricity  from  some  outside 
source,  through  the  cell.  The  direction  of  the  charging 
current  is,  of  course,  opposite  to  that  during  discharge.  A 
storage  battery,  then,  is  not,  as  most  people  believe,  a  reser- 
voir, into  which  electricity  can  be  pumped  and  held  for 
a  time  then  drawn  off  as  desired.  What  is  actually  stored 
in  the  cell  is  not  electricity,  but  chemical  energy  in  a  poten- 
tial state.  With  this  fact  clearly  fixed  in  mind,  the  opera- 
tion and  care  of  storage  batteries  becomes  a  comparatively 
simple  matter. 

While  there  are  several  kinds  of  materials,  which  can 
be  employed,  the  combination  most  universally  used  is  that 
of  lead  plates  in  an  electrolyte  of  dilute  sulphuric  acid. 
The  active  material  on  the  positive  plate  is  peroxide  of  lead 
(Pb  O2),  and  on  the  negative,  spongy  lead  (Pb).  The 
plates  usually  consist  of  a  cast  lead  framework  or  grid,  hav- 
ing many  pockets,  which  are  filled  with  the  active  material. 
Several  of  both  kinds  of  plates,  always  one  more  negative 

11 


Ignition 

than  positive,  are  alternately  assembled  together,  but  insu- 
lated one  from  another  by  thin  strips  of  rubber  or  wood,  the 
positive  and  negative  plates  being  respectively  connected  to 
the  positive  and  negative  terminals  of  the  cell.  In  the  igni- 
tion type  of  batteries  there  are  usually  three  positive  and 
four  negative  plates,  the  capacity  of  the  cell  depending  upon 
the  total  area  of  the  plates.  The  containing  jars  are  glass 
or  hard  rubber  and  the  electrolyte  is  a  ten  per  cent  solution 
of  sulphuric  acid  in  distilled  water.  A  good  storage  battery 
will  last  for  several  years  if  properly  cared  for,  but  it  must 
be  guarded  against  several  diseases  to  which  it  is  susceptible. 

I  EDISON  STORAGE  BATTERY. 

How  about  the  new  Edison  storage  battery  upon  which 
the  great  inventor  has  been  experimenting  the  last  eight 
years  at  an  enormous  expense  ?  It  is  undoubtedly  a  success, 
and,  were  it  not  for  the  excessively  high  cost  of  production, 
would  soon  replace  the  lead  cell,  being  free  from  the  list  of 
diseases  which  beset  the  lead  battery.  The  active  elements 
are  oxides  of  nickel  and  iron  in  an  electrolyte  of  potassium 
hydrate  (KOH). 

The  grids  are  made  of  nickel-plated  pressed  steel,  the 
positive  containing  nickel  oxide  mixed  with  flaked  metallic 
nickel,  the  latter  material  reducing  the  resistance  of  the 
oxide.  The  negative  grid  contains  iron  oxide,  commonly 
known  as  iron  rust,  and  the  containing  cans  are  made  of 
nickel-plated  steel,  having  all  seams  welded.  This  cell  will 
stand  a  great  deal  of  abuse. 


12 


Chapter  Two 

Electrical  Units  and  Laws  Governing 
the  Flow  of  Electricity 

In  the  preceding  chapter  a  few  general  principles  of 
electricity  were  discussed.  Consider  now  a  few  laws  which 
govern  its  rate  of  flow,  and  learn  how  an  understanding  of 
these  laws  can  aid  us  in  the  proper  installation  and  care  of 
batteries.  We  have  seen  that  there  are  two  conditions  that 
must  be  fulfilled  before  a  current  of  electricity  can  be  pro- 
duced, namely,  a  complete  circuit,  composed  wholly  of  con- 
ductors, and  included  as  a  part  of  that  circuit,  some  source 
— or  sources — of  Electro-Motive-Force. 

VOLT. 

The  unit  of  E.  M.  F.  is  called  the  Volt,  and  represents  a 
certain  specific  amount  of  that  force  zuhich  tends  to  move 
electricity.  The  volt,  therefore,  signifies  electrical  pressure 
only,  and  does  not  designate  any  particular  quantity  of  elec- 
tricity. 

AMPERE. 

The  unit  of  volume  or  size  of  an  electric  current  is 
called  the  Ampere  and  represents  a  certain  specific  rate  of 
How.  The  ampere,  therefore,  signifies  volume  of  current 
only,  and  not  any  particular  quantity  of  electricity.  Volts 
correspond  to  pounds  pressure  in  a  water  pipe,  and  amperes 
to  the  size  or  volume  of  the  stream. 

13 


Ignition 

AMPERE  HOUR. 

In  order  to  measure  any  particular  quantity  of  current 
electricity,  we  must  introduce  the  factor  of  time.  Static 
electricity  can  be  stored,  that  is,  held  for  a  while  in  con- 
densers, and  its  quantity  then  measured ;  but  not  so  with 
current  electricity.  If  a  fixed  number  of  amperes  flows  past 
a  given  point  in  a  wire  for  a  definite  period  of  time,  a  cer- 
tain specific  quantity  of  electricity  will  have  passed  that 
point.  The  unit  quantity  of  electricity  is  determined  when 
one  ampere  flows  for  one  second,  and  is  called  a  cou- 
lomb. As  the  coulomb  is  a  very  small  unit,  it  has  been  re- 
placed, in  practical  work,  by  the  ampere-hour,  which  is  one 
ampere  flowing  for  one  hour,  or  the  equivalent.  One  am- 
pere-hour, then,  equals  3,600  coulombs. 

We  have  already  pointed  out  that  electricity  can  only 
pass  through  certain  substances  known  as  conductors  and 
not  through  others  called  insulators.  Further  experimenting 
would  have  disclosed  the  fact  that  there  is  no  such  thing  as 
a  perfect  conductor*  or  perfect  insulator,  and  that  the 
power  of  conducting  electricity  by  different  materials  greatly 
varies.  Silver  is  the  best  known  conductor,  but  even  it 
offers  some  opposition  to  an  electric  current.  Therefore, 
when  a  current  is  forced  through  a  conductor,  the  attending 
"friction"  produces  heat,  and,  if  sufficient  current  is  used, 
the  conductor  can  actually  be  melted. 

OHM. 

Since  a  current  encounters  resistance  in  its  passage 
through  a  conductor,  it  is  easy  to  see  that  a  given  E.  M.  F. 


*An  Electron — the  absolute  unit  of  electricity — may  be  a  perfect  con- 
ductor within  itself.  For  an  interesting  and  authoritative  treatise  on  this 
and  similar  subjects,  see  "Electrons,"  by  Sir  Oliver  Lodge,  D.  Sc.,  F.  R.  S., 
and  also  "Electricity  and  Matter,"  by  Sir  J.  J.  Thomson,  D.  Sc.,  F.  R.  S. 

14 


Electrical  Units  and  Laws  Governing  the  Flow  of  Electricity 

is  capable  of  forcing  a  given  current  through  only  a  certain 
definite  resistance.  The  logical  unit  of  resistance,  therefore, 
is  that  amount  of  resistance  through  which  a  pressure  of 
one  volt  can  force  a  current  of  one  ampere,  and  is  called 
the  Ohm. 

WATT. 

One  other  unit  must  be  mentioned,  namely,  that  of 
electrical  energy  or  power.  It  is  easy  to  see  that  a  cer- 
tain current,  propelled  by  a  high  E.  M.  F.,  repre- 
sents more  power  than  the  same  current  propelled  by 
a  low  E.  M.  F.  The  unit  of  electrical  power,  therefore,  is 
that  amount  of  power  exerted  when  one  ampere  Hows  under 
a  pressure  of  one  volt,  and  is  called  a  Watt.  It  follows  that 
a  watt  is  a  volt-ampere,  and  that  the  power  in  watts  exerted 
in  a  direct  current  circuit  is  equal  to  the  total  number  of 
volts  multiplied  by  the  amperes,  acting  in  that  circuit.  The 
readings  of  voltage  and  amperage  must,  of  course,  be  taken 
simultaneously.  This  relation  can  be  expressed  algebraic- 
ally thus : 

W  =  I  E (1) 

where  W  stands  for  watts,  /  for  amperes,  and  E  for  volts. 

Having  clearly  fixed  in  mind  the  meaning  and  values  of 
these  various  units,  their  numerical  relations  can  be  dis- 
cussed. 

OHM'S  LAW. 

Many  years  ago,  Dr.  Ohm,  after  whom  the  unit  of 
resistance  was  named,  discovered  that,  in  a  circuit  of  con- 
stant resistance  the  current  increases  as  the  voltage  is  in- 
creased; and  with  a  constant  E.  M.  F.  the  current  decreases 
as  the  resistance  is  increased.  This  fact  is  known  as  "Ohm's 
Law"  and  is  the  fundamental  law  of  electricity,  since  it 

15 


Ignition 

governs  the  rate  of  current  flow  in  direct  current  circuits. 
Its  importance,  therefore,  cannot  easily  be  over-estimated. 
Ohm's  Law  may  be  stated  as  follows: 

The  current  in  a  direct  current  circuit  varies  directly 
as  the  total  E.  M.  F.  and  inversely  as  the  total  resistance 
acting  in  that  circuit; 

or: 

E.  M.  F.  in  volts 
•   Strength  of  current  in  amperes  =  - 


resistance  in  Ohms 
and  expressed  algebraically : 
E 

/  =  - (2) 

R 

where  R  stands  for  Ohms.  By  simple  transposition  we  have : 
E 

*W- (3) 

/ 
and 

E  =  IR (4) 

It  is   evident   that   if  two  of   the   factors   are   known,   the 
third  can  easily  be  calculated.  s.v 

SERIES  CONNECTIONS. 

A  word  now  about  series  and  parallel  circuits  before 
we  take  up  the  practical  application  of  these  principles.  If 
we  join  a  number  of  conductors  together,  end  to  end,  in  a 
circuit,  so  that  the  entire  current  will  have  to  pass  through 
each  one  successively,  they  are  said  to  be  connected  in  series, 

16 


Electrical  Units  and  Laws  Governing  the  Flow  of  Electricity 


DIAGRAM    NO.I 

SERIES      CONNECTIONS 

18    VOITS- 


L/IMP 
POWEft-t£x/Q- 


WATTS 


and  it  is  obvious  that  the  total  resistance  will  be  the  sum  of 
their  respective  resistances.  Series  connections  are  illus- 
trated in  diagram  No.  1. 

PARALLEL  CONNECTIONS. 

If,  on  the  other  hand,  we  connect  several  conductors 
together,  so  as  to  provide  a  number  of  separate  paths 
through  which  the  current  can  flow  from  one  point  to 


DIAGRAM 

MULTIPLE 


N0.2 


I  AMP    REQV/RE5     .£  AMP.   AT  6  VOLTS 
-    /.£  X  6  -  9    WATTS 


another,  they  are  said  to  be  joined  in  parallel  or  multiple; 
and  each  separate  conductor  is  known  as  a  Shunt  on  the 
others.  Multiple  connections  are  shown  in  diagram  No.  2. 

JOINT  RESISTANCE. 

To  figure  the  joint  resistance  of  several  conductors,  con- 
nected in  multiple,  as  between  points  "A"  and  "B"  in  dia- 


17 


Ignition 


VlftGRKM    NO  5. 

"R=  5    OHMS 

A     A     A    A. 

N 

—  vvw  

s\ 

60AMP 

•R=li>   OHMS 

60/^MP. 

ft 

/        V  Wv 

la   flMPETR  ES 

B 

B  -  3O    OHMS 

*£SPECT,V£   6loNDllST»NCt5»KS±^0»HJ>3\ 

WHICH      ABE    TO    E/1CH      0THET?    flS   6,  3  /1NX>  1 

gram  No.  3,  first  find  the  joint  conductance  by  adding  the 
respective  conductances  of  the  various  branches;  the  word 
"conductance"  meaning  the  precise  opposite  of  resistance, 
and  equal  numerically  to  the  reciprocal  of  the  resistance  in 
ohms.  The  joint  resistance,  of  course,  is  the  reciprocal  of 
the  joint  conductance.  Therefore,  the  joint  resistance  in 
ohms  of  a  number  of  conductors  joined  in  multiple,  is  equal 
to  the  reciprocal  of  the  sum  of  their  respective  conductances. 
For  example  to  find  the  joint  resistance  between  points  "A" 
and  "B",  the  resistance  of  the  various  shunts  is  respectively 
5,  10  and  30  ohms.  Therefore,  their  conductances  are  1/5, 
1/10  and  1/30,  which,  added  together,  equal  the  joint  con- 
ductance of  1/3.  The  reciprocal  of  their  joint  conductance 

3 
is  —  or  3.    Hence,  the  joint  resistance  is  3  ohms. 

1 

CURRENT  IN  BRANCH  CIRCUITS. 

Referring  again  to  diagram  No.  3 ;  notice  that  the  cur- 
rent flowing  from  the  battery  divides  when  it  reaches 
point  "A"  and  part  of  it  flows  through  each  branch,  the  cur- 
rent, of  course,  dividing  in  direct  proportion  to  the  conduct- 

18 


Electrical  Units  and  Laws  Governing  the  Flow  of  Electricity 

ances  of  the  several  branches.  ,  This  .principle  is  used  to 
advantage  in  the  multiple  connecting  of  batteries. 

We  have  discussed  these  various  electrical  units  and  their 
relations  to  one  another  at  considerable  length,  because  we 
wish  to  urge  upon  the  reader  the  importance  of  his  becom- 
ing thoroughly  familiar  with  these  fundamental  principles, 
especially  Ohm's  Law,  for  he  will  find  that  a  knowledge  of 
the  basic  principles  involved,  along  with  a  little  thought,  is 
all  that  is  needed  to  make  the  locating  and  correcting  of 
faults  in  his  electrical  equipment  a  very  simple  matter. 

RESISTANCE  OF  DIFFERENT  MATERIALS. 

The  table  herewith,  shows  the  approximate  re- 
sistance of  different  materials,  as  compared  with  that 
of  pure  copper,  which  is  taken  as  "I". 

Since  there  is  no  known  perfect  insulator,  we  can, 
according  to  Ohm's  Law,  force  a  current  through  even  the 
best  insulator,  provided  we  sufficiently  increase  the  voltage, 
but,  when  this  is  done,  the  current  takes  the  form  of  a  jump 
spark  and  burns  its  way  through  the  insulator,  thereby  de- 
stroying it.  This  phenomenon  is  known  as  "disruptive  dis- 
charge" and  is  what  takes  place  between  the  points  of  a 
spark  plug  in  the  jump  spark  system  of  ignition. 


19 


20 


Electrical  Units  and  Laws  Governing  the  Flow  of  Electricity 


TABLE  OF  COMPARATIVE  RESISTANCES. 


(MATTHIESSEN'S  STANDARD.) 


COPPER  =  i. 

RELATIVE 
MATERIALS.  RESISTANCE. 

Silver   annealed    0.925] 

Copper    1.00     \ 

Gold   (99%    pure) 1.38 

Aluminum    (99%   pure) 1.61    J 


GOOD 
CONDUCTORS 


Zinc    3.62 

Platinum,  annealed    5.65 

Iron     5.70 

Nickel 7.78 

Tin    8.28 

Lead    12.8 

Antimony 22.1 

Mercury 59.3 

Bismuth    82.2 

Carbon    (arc   light)    2510.0 


FAIR 
CONDUCTORS 


Sea  water   

Ordinary  water    

Dampness    

Damp   wood    

Partly  carbonized  oil.  . 
Dirt  of  any  kind,  etc. 


Leather,     cured     

Ordinary   dry   wood 

Black    vulcanized    or    hard    fibre. 
Red    fibre    


POOR 
CONDUCTORS 


POOR  INSULATORS  FOR  VOLT- 
AGES HIGHER  THAN  1,000 
BUT   FAIRLY  GOOD   FOR 
LESS  VOLTAGE 


White  vulcanized   or  hard  fibre 

Ditto — Boiled   in    paraifine 

Kiln  dried  wood   

Ditto — Boiled    in    paraffine 

"Electros"    or    composition    materials.... 

Asbestos    (dry)    

Various  dry  oils 

"Empire"    oiled    fabrics. .  ,  , 

Card  board  and  paper  boiled  in  paraffine 

Shellac    (dry)     

Insulating    varnishes    

Micanite   cloth    and    paper 

Rubber    (soft)    

Rubber    (hard)    

Porcelain     

Paraffine,  beeswax,   rosin,  etc 

Sulphur     

Glass     

Mica    . 


GOOD 
INSULATORS 


21 


Chapter  Three 

Connecting,  Testing  and   Care 
of  Batteries 

Consider  now  the  purely  practical  side  of  the  subject. 
Suppose  one  wants  to  buy  some  dry  batteries.  He  should 
not  accept  any  cell  the  clerk  in  the  store  gives  him.  He 
ought  first  to  ask  for  some  well-known  make.  Then  look 
at  the  date  stamped  on  the  cell,  and,  if  it  is  several  months 
old,  the  chances  are  ten  to  one  that  the  small  amount  of 
moisture  or  electrolyte  originally  in  the  cell  is  already  half 
dried  up. 

TESTING  DRY  CELLS. 

After  finding  a  cell,  bearing  a  recent  date,  test  it  for 
amperage  with  a  pocket  "battery  tester"  or  ammeter,  which 
should  have  been  previously  compared  with  a  larger  instru- 
ment for  accuracy.  Hold  the  ammeter  in  contact  only  the 
fewest  possible  seconds  necessary  to  obtain  a  reading,  for, 
since  the  resistance  of  the  ammeter  is  extremely  low — in 
fact  practically  nothing — the  cell  while  being  tested  is  dis- 
charging at  its  maximum  possible  rate. 

The  cell  showing  the  highest  amperage  is  not  neces- 
sarily the  best.  This  reading  is  not  an  indication  of  the 
amount  of  electricity  in  the  cell,  but,  rather  of  the  highest 
possible  rate  of  chemical  action  that  the  active  elements  and 
the  depolarizer  can  undergo.  By  the  use  of  extra  strong 

22 


Connecting,  Testing  and  Care  of  Batteries 

chemicals  in  the  construction,  a  standard  No.  6  cell  can  be 
made  to  show  40  amperes  or  more,  but,  when  this  is  done, 
the  chemicals  will  soon  burn  themselves  out,  without  doing 
useful  work,  and  greatly  reduce  the  life  of  the  cell.  It  has 
been  found  that  the  combination  of  chemicals  best  suited 
for  long  life  and  efficiency,  under  ordinary  conditions,  in  the 
standard  No.  6  cell,  is  that  which  will  cause  the  latter  to  test 
16  to  20  amperes.  However,  this  may  vary  slightly  with  dif- 
ferent good  makes  of  cells.  As  severe  cold  temporarily 
checks  chemical  action,  dry  cells  will  not  show  their  full 
strength  when  chilled  through ;  and,  on  the  other  hand,  cells 
should  not  be  kept  too  warm,  as  their  chemical  action  would 
be  unduly  stimulated,  thereby  shortening  their  life. 

Should  we  be  without  an  ammeter,  a  rough  test  can  be 
made  by  holding  a  nail  or  a  key  firmly  against  the  zinc 
binding  post,  screwed  up  tight,  and  touching  the  surface  of 
the  carbon  rod  with  the  smallest  point  possible.  Owing  to 
the  high  contact  resistance  of  carbon,  if  the  cell  is  quite  new, 
a  tiny  red  spark  or  arc,  accompanied  by  a  little  puff  of 
smoke,  will  form  at  the  point  of  contact;  if,  however,  just 
a  little  black  ring  forms  on  the  carbon  around  the  point  of 
contact,  there  is  some  life  left,  sufficient  usually  to  run  the 
engine  a  few  hours  at  least.  With  a  little  experience,  a 
fairly  accurate  test  can  be  made  in  this  way.  If  a  cell  in  a 
set  will  not  pass  this  test,  or  show  4  or  5  amperes  on  an 
ammeter,  it  is  dead  and  should  be  thrown  out,  as  it  adds 
to  the  resistance  of  the  circuit,  and  thereby  tends  to  check 
the  current  flow  from  the  rest  of  the  cells. 

E.  M.  F.  OF  CELLS. 

The  E.  M.  F.  of  a  primary  cell  depends  upon  the  charac- 
ter of  the  active  elements,  and  not  upon  the  size  of  the  cell. 

23 


Ignition 

Dry  cells,  regardless  of  size,  should,  when  new,  show  about 
1.5  volts,  which  figure,  however,  is  rarely  ever  reduced  even 
to  1.2  when  the  cell  is  exhausted,  provided  the  reading  is 
taken  on  "open  circuit,"  viz. :  when  there  is  no  current 
being  drawn  from  the  cell.  The  voltage  of  an  exhausted 
cell  will,  however,  drop  to  nearly  nothing  the  instant  an 
attempt  is  made  to  draw  a  current  from  it.  An  ammeter, 
however,  is  much  to  be  preferred  in  ascertaining  the  condi- 
tion of  dry  cells. 

AMPERAGE  OF  CELLS. 

The  amperage,  which  can  be  drawn  from  a  cell,  in- 
creases directly  with  the  size  or  rather  the  area  of  the  active 
elements.  Should  we  find  ourselves  dependent  for  a  few 
hours  run  upon  a  newly  exhausted  set  of  dry  cells,  we  can 
coax  them  into  action  for  a  while  longer  by  breaking  out  the 
sealing  wax  on  the  top  and  pouring  in  as  much  water  as 
will  be  absorbed,  as  this  tends  to  reduce  the  internal 
resistance.  The  internal  resistance  of  a  No.  6  dry  cell, 
when  new,  is  about  0.064  ohm. 

In  setting  up  wet  or  liquid  cells,  follow  the  directions 
given  by  the  maker,  being  careful  not  to  get  any  dirt  into 
the  electrolyte. 

TESTING  STORAGE  BATTERIES. 

An  ammeter  should  never  be  used  to  test  a  storage  bat- 
tery, for,  owing  to  the  extremely  low  internal  resist- 
ance of  both,  a  current  of  100  or  200  amperes  would  flow, 
which  would  not  only  wreck  the  ammeter,  but  ruin  the 
plates  of  the  cells  as  well.  A  low  reading  voltmeter  should 
be  used  to  test  storage  batteries,  and  should  show  two  volts 
per  cell  when  pretty  well  charged,  and  when  the  voltage  per 
cell  drops  to  about  1.8,  it  should  be  recharged.  The  voltage 

24 


Connecting,  Testing  and  Care  of  Batteries 

should  never  be  allowed  to  drop  below  1.7.  These  readings 
should  be  taken  when  the  battery  is  discharging  under  nor- 
mal conditions.  A  lead  storage  battery  should  not  remain 
long  in  an  uncharged  condition,  as  lead  sulphate  (Pb  SO4) 
will  form  on  the  plates.  As  this  material  has  a  high  resist- 
ance, it  tends  to  insulate  the  plates  from  the  electrolyte, 
thereby  greatly  increasing  the  internal  resistance  of  the 
battery,  which,  of  course,  reduces  the  available  current. 
This  process  is  known  as  "sulphation,"  and  is  the  most 
common  disease  of  the  lead  battery.  The  remedy  for  a 
mild  case  of  sulphation  is  a  very  long  charge  at  about  one- 
fourth  or  less  of  the  normal  charging  rate. 

INSTALLING  BATTERIES. 

A  word  upon  the  installing  of  batteries.  Referring  to 
the  table  of  comparative  resistance  of  materials  notice  that 
water,  dampness,  and  dirt  of  any  kind  are  partial  conductors. 
Therefore,  to  avoid  leakage  and  consequent  waste  of  cur- 
rent, install  the  batteries  in  a  clean,  dry,  cool,  but  not  cold, 
place,  as  free  from  vibration  as  possible.  If  dry  cells  are 
used,  nail  together  several  strips  of  wood  to  separate  the 
cells  one  from  another,  and  hold  them  off  the  bottom  of  the 
box  in  which  they  are  placed.  It  is  a  good  plan  to  boil  the 
strips  of  wood  in  paraffine,  or,  at  least,  to  give  them  a  good 
coat  of  shellac,  as  this  prevents,  them  from  absorbing 
moisture. 

If  the  regular  portable  type  of  storage  battery  is  used,  it 
should  frequently  be  thoroughly  rinsed  with  cold  water,  by 
placing  it  under  the  faucet,  and  then  wiped.  Be  sure 
that  the  rubber  corks  are  in  place,  so  that  no  water  or 
dirt  will  get  washed  into  the  electrolyte.  During  the  process 
of  charging,  a  storage  battery  gives  off  a  certain  amount  of 

25 


Ignition 


acid  spray,  which,  if  allowed  to  remain,  rapidly  corrodes  the 
terminals  and  destroys  the  wooden  case.  No  trouble  need 
be  experienced  from  the  acid,  if  the  battery  is  thoroughly 
washed  after  each  charge,  or  oftener.  Cleanliness  is  the 
main  thing  to  observe  in  the  care  of  batteries. 

In  connecting  cells  together,  flexible  conductors  should 
be  used,  or  better  yet,  the  little  copper  battery  connectors 
that  are  made  for  the  purpose.  Be  sure  to  see  that  the  bind- 


-NO. 4. 


SERIES     CONNECTIONS. 


OPEN  C1R6UI T  VOL  TAGE  AB OUT  /. 


>$£  RIES-MULTI  PLE       CONNECTIONS. 


WORKING  VOL  TA6E  JBOUT   6.S 
C/ffGU/r  VOLTJ6£   ABOUT      7.3~ 


26 


Connecting,.  Testing  and  Care  of  Batteries 

ing  nuts  are  tight,  and  particularly  that  the  screw  attached 
to  the  carbon  rod  in  a  dry  cell  is  very  tight,  so  as  to  reduce 
the  contact  resistance  of  the  carbon  to  a  minimum. 

A  loose  contact  with  the  carbon  rod  is  a  fault  often  very 
troublesome  to  locate,  for  it  does  not  completely  shut  off 
the  current,  as  does  a  broken  wire,  but,  owing  to  the  high 
resistance,  permits  only  a  part  of  the  current  to  flow. 

When  several  cells  are  joined  together,  to  form  a  single 
source  of  E.  M.  F.,  the  whole  is  called  a  battery.  It  is  well 
to  use  cells  of  the  same  make  and  necessary  that  they  be  of 
the  same  age  and  in  the  same  condition.  It  is  not  economy 
to  connect  a  new  cell  with  several  old  ones. 

VOLTAGE  AND  AMPERAGE  OF  SET  OF  CELLS. 

When  cells  are  connected  in  series,  and  the  entire  cur- 
rent thereby  made  to  flow  through  each  one  successively,  it 
is  easy  to  see  that  no  more  current  or  amperage  can 
economically  be  drawn  from  the  set  than  from  one  cell. 
The  E.  M.  F.,  however,  will  be  increased  as  the  current  pro- 
ceeds from  one  cell  to  the  next ;  therefore,  the  total  voltage 
of  a  number  of  cells  connected  in  series  is  equal  to  the  sum 
of  the  voltage  of  the  separate  cells  and  the  total  amperage 
is  no  greater  than  that  of  one  cell. 

It  is  important  that  we  learn  the  voltage  best  suited 
economically  to  operate  our  electrical  apparatus ;  this  infor- 
mation can  best  be  had  from  the  manufacturers.  While 
most  ignition  apparatus  is  designed  for  use  with  six  volts, 
there  is  some  apparatus  which  requires  eight,  and  others 
work  more  satisfactorily  and  efficiently  on  four.  Taking  1.5 
volts  per  dry  cell,  we  see  that  four  cells  in  series  will  give 
an  E.  M.  F.  of  six  volts,  but,  because  the  internal  resistance 

27 


Ignition 

of  dry  cells  increases  as  the  cells  are  used,  reducing  the 
available  or  working  E.  M.  F.,  five  cells  instead  of  four, 
are  usually  used  for  six-volt  apparatus. 

Since  the  life  of  a  dry  cell  depends  almost  entirely  upon 
the  rate  of  discharge,  it  is  desirable  to  keep  the  current  flow- 
ing through  the  cells,  as  low  as  practicable.  By  connecting 
a  number  of  batteries,  of  equal  voltage,  in  multiple,  the  cur- 
rent divides,  as  we  have  seen,  and  only  a  part  flows  through 
each  branch,  thereby  reducing  the  demand  on  each  battery. 

CURRENT  FROM  CELLS  IN  MULTIPLE. 

The  number  of  amperes  flowing  in  a  circuit  governs  the 
number  of  sets  of  cells  to  be  connected  in  multiple.  A  low 
reading  ammeter  should  be  included  in  the  main  circuit  to 
show  the  amperage,  and  a  sufficient  number  of  batteries 
should  be  placed  in  multiple  to  reduce  the  current  in  each 
branch  to  J4  ampere,  or  less,  if  they  are  to  work  on  closed 
circuit,  as  in  operating  electric  lights.  This  is  illustrated  in 
diagram  No.  4. 

The  demand  for  current  made  by  a  single-cylinder  en- 
gine, if  an  efficient  coil  is  used,  is  not  too  great  to  be  effi- 
ciently furnished  by  one  set  of  cells  in  series.  For  operat- 
ing multiple  cylinder  engines,  much  more  efficiency  is  to  be 
had  from  ten  cells,  connected  in  series-multiple,  than  if  they 
were  used  in  two  separate  sets  of  five  in  series.  It  would  be 
well  to  have  as  many  sets  in  multiple  as  there  are  cylinders, 
but  this  is  often  impracticable. 

The  results  of  many  careful  tests,  made  to  show  the  in- 
crease in  efficiency  of  dry  cells,  when  connected  in  series- 
multiple,  are  given  below.  Tests  were  made  on  a  four- 
cylinder  automobile  engine,  in  severe  service,  as  well  as  in 
many  other  ways. 

28 


Connecting,  Testing  and  Care  of  Batteries 

TESTS  OF  CELLS  IN  MULTIPLE. 

When  dry  cells  are  connected  in  series-multiple,  four  in 
series  will  usually  have  sufficient  working  voltage  to  operate 
six-volt  apparatus,  since  the  internal  resistance  of  a  battery, 
composed  of  cells  in  series-multiple,  is  much  less  than  in  one 


RESULTS  OF  PRflCT/C/IL  TEST  0N  D1RV     CELLS. 

c 

2 
3 
4 

HOURS    seRVjce 

>          2O         40.         6O         SO         /<*?       120         140         160         180 

— 

NO. 

WRftNGEMENT  OF  DT^r    CELL  S. 

I 

SET    OF4JN     SEKIES. 

2 

2  SETS    OF  4-  »W      SE"RI£S-MULTIPL£. 

3 

3  SETS   OF  4  IN     SERIES-MULTIPLE. 

4 

4SET5  OF  4  IN     SEtt/HS-MULTlPLE. 

set  of  cells  in  series.  For  some  apparatus,  however,  par- 
ticularly electric  lights  on  closed  circuit,  it  is  well  to  have 
the  battery  composed  of  sets  of  five  cells  in  series,  which 
will  insure  an  average  working  E.  M.  F.  of  about  six  volts. 


29 


Chapter  Four 

The  Simplest  Form  of  Electric 
Ignition 

Having  a  fairly  good  idea  of  an  electric  current,  its 
production  in  galvanic  batteries  and  mode  of  travel,  we  shall 
now  see  how  it  ignites  the  charge  in  gas  engines.  Clearly 
fix  in  mind  just  what  the  requirements  are. 

First — The  work  must  be  done  inside  the  cylinder,  and 
consequently  the  current  must  be  led  through  the  cylinder 
walls ;  this  must  be  accomplished  without  leaving  any  cracks 
or  leaks  through  which  the  gas  can  escape. , 

Second — Enough  heat  must  be  developed  to  instantly 
ignite  the  charge  under  all  conditions. 

Third — The  ignition  must  occur  at  a  certain  fixed  time, 
without  a  variation  of  so  much  as  a  hundredth  or  even  a 
thousandth  part  of  a  second. 

Fourth — The  apparatus  must  be  very  reliable  and  there- 
fore simple. 

Fifth — It  must  be  efficient. 

Electric  ignition  may  be  divided  into  two  general  classes 
— the  Jump  Spark  or  High  Tension,  and  the  Touch  Spark  or 
Low  Tension  systems.  We  will  confine  ourselves  in  this 
chapter  to  the  Touch  Spark  system. 

MAKE  AND  BREAK  IGNITION. 

There  are  three  principal  parts  to  Touch  Spark  ignition, 
namely,  a  source  of  E.  M.  F.,  a  Touch  Spark  or  Primary 
coil,  and  an  Igniter. 

30 


The  Simplest  Form  of  Electric  Ignition 


The  source  of  E.  M.  F.  may  be  any  suitable  galvanic 
battery  of  usually  four  to  six  volts,  such  as  a  set  of  four  or 


Photograph    showing   magnetic   field,   generated   around   a   copper   wire   carrying 

a  current  of  120  amperes.     The  wire  passes  through  a  piece  of  paper  and 

the  magnetic  lines  are  formed  by  iron  filings  sprinkled  on  the  paper. 

five  dry  cells ;  or  a  low  tension  Dynamo  or  Magneto.  In 
some  special  forms  of  magnetos,  the  primary  coil  is  com- 
bined with  the  armature  of  the  machine  itself.  This  latter 
system  will  be  described  in  detail  in  the  last  chapter. 

Before  the  action  of  the  Touch  Spark  coil  can  be  under- 
stood, mention  must  be  made  of  a  most  important  charac- 
teristic of  current  electricity. 

An  electric  current  does  not  confine  its  influence  solely 
to  the  conductor  through  which  it  passes,  but  sets  up  a  kind 
of  rotary  disturbance,  in  the  nature  of  whirls,  at  right  angles 

31 


Ignition 


Series    of    diagrams    showing    various    steps    in    increasing    the    magnetic    field 

surrounding   a    current   carrying   wire.      With    a    properly   constructed   coil 

as    in    Diagram    4    the    apparent    momentum    of    the    current    can    be 

increased    many    times,    which    results    in    a    hot    spark    when    the 

circuit    is   broken. 


Diagram   No.    1 

Shows  the  beginning  of  the 
magnetic  lines  forming  around 
the  wire  instantly  after  the 
circuit  is  closed. 


Diagram  No.  2 

Shows  how  the_magnetic  lines 
combine    an    instant    later. 


Diagram   No.    3 
Shows     how     the     magnetic     density     is     increased     by 
placing     a     piece     of    iron     in     the     center 
of  the  coil. 

32 


The  Simplest  Form  of  Electric  Ignition 


N 


Diagram   No.    4 

Shows   how   the   magnetic    density    is   still    further    in- 
creased  by   placing    the   coil    in   an   iron   box- 

to  and  around  the  wire,  in  the  all-pervading  Ether-of- 
Space.1  This  phenomenon  is  the  same  as  that  near  the  poles 
of  an  ordinary  magnet  and  is  known  as  Magnetism ;  in  other 
words,  an  electric  current  magnetizes  the  space  around  it. 

ELECTRIC  INERTIA  AND  MOMENTUM. 
When  a  circuit  is  completed,  the  current  starts  to  flow, 
but  is  held  back  for  an  instant  by  its  growing  magnetic  field, 
and  consequently  does  not  reach  its  full  value,  as  determined 
by  Ohm's  Law,  until  its  magnetic  field  has  ceased  to  grow 
and  become  constant ;  and,  conversely,  a  current  does  not 
instantly  stop  on  breaking  a  circuit,  but  is  maintained  for  a 
moment  by  the  collapsing  or  shrinking  of  the  magnetic  lines. 
An  electric  current,  therefore,  appears  to  possess  inertia  and 
momentum,2  and  it  is  this  tendency  to  persist  or  apparent 

1  See   an   article   by   the   author   in    POWER   BOATING   for   July   and  August, 
1910. 

2  (For    an    interesting    and    non-mathematical    treatise    on    Electricity    and 
Magnetism,  see  "Modern  Views  of  Electricity,"  by  Sir  Oliver  Lodge,  F.  R.  S. 
This   book  is   obtainable   through  The   Penton   Publishing    Co.,    Cleveland,   O.) 

33 


Ignition 

momentum  of  an  electric  current  which  causes  it  to  burst 
through  the  intervening  air  space,  thus  producing  the  spark 
seen  on  breaking  a  circuit.  This  is  the  way  the  spark  is 
produced  in  make-and-break  ignition. 

MAGNETIC  FIELD. 

The  magnetic  field  around  a  current-carrying  wire  can 
be  shown  by  sprinkling  iron  filings  on  a  cardboard,  through 
which  the  wire  is  passed  at  right  angles.  Since  magnetism 
finds  a  much  easier  path  through  iron  than  air,  the  filings 
will  arrange  themselves  in  concentric  circles  around  the 
wire,  as  the  photograph  shows. 

In  order  to  secure  a  large,  "fat"  spark,  when  the  circuit 
is  broken,  the  apparent  momentum  of  the  current  must  be 
increased,  which  can  be  done  by  increasing  the  surrounding 
magnetic  field.  This,  in  turn,  can  be  accomplished  by  wind- 
ing the  wire  into  a  compact  coil,  making  the  current  circulate 
around  a  small  space  many  times,  thereby  greatly  concen- 
trating the  magnetism.  In  this  case  the  magnetic  lines 
around  each  turn  of  wire  tend  to  open  up  and  include  the 
other  turns.  The  magnetic  density  can  still  further  be  in- 
creased by  placing  a  piece  of  iron  in  the  center  of  the  coil. 
With  a  properly  constructed  coil  of  this  kind,  the  apparent 
momentum  of  a  current  can  be  increased  many  times,  re- 
sulting in  a  fat,  hot  spark  when  the  circuit  is  broken. 

THE  IGNITER. 

The  igniter  is  simply  a  means  for  making  and  breaking 
an  electric  circuit  inside  the  cylinder,  and  usually  consists 
of  two  electrodes,  insulated  from  each  other,  one  fixed  in 
position  and  the  other  moveable  into  and  out  of  contact 
with'  it.  Usually  a  lever,  extending  from  some  moving  part 

34 


The  Simplest  Form  of  Electric  Ignition 

of  the  engine,  engages  the  moveable  electrode,  causing  a 
separation  at  the  instant  ignition  is  required. 

Having  now  a  general  idea  of  the  theory  of  make-and- 
break  ignition,  we  will  in  the  next  chapter  turn  our  atten- 
tion to  the  practical  construction  and  operation  of  its  parts. 


35 


Chapter  Fvie 

Construction  and   Operation  of 
Make-and-Break   Coils 

The  Make-and-Break  coil  consists  of  a  few  hundred 
turns  of  insulated  copper  wire,  varying  in  size  from  No.  14 
to  20  B.  &  S.  gage,  wound  around  an  iron  core,  about  an 
inch  in  diameter,  and  from  3  to  10  inches  long.  Since  mag- 
netism does  not  penetrate  to  the  center  of  and  saturate  a 
thick  bar  of  iron  as  readily  as  a  thin  one,  the  core  is  made  up 
of  a  bundle  of  small  iron  wires.  If  the  best  results  are  to  be 
obtained,  the  iron  wires  must  be  thoroughly  annealed,  to 
make  them  as  soft  as  possible,  otherwise  the  magnetic 
lines  cannot  easily  rise  and  fall  through  them.  The  turns 
of  copper  wire  must  be  well  insulated  one  from  another,  to 
prevent  leakage  or  short-circuits. 

Some  kinds  of  Make-and-Break  coils  are  placed  in  an 
iron  box,  which  provides  a  nearly  complete  circuit  of  iron, 
through  which  the  magnetic  lines  can  pass.  This  tends  to 
increase  the  time  required  for  the  magnetic  field,  and  conse- 
quently the  current,  to  build  up  to  its  maximum.  In  this 
construction,  however,  a  small  space  should  be  left  between 
the  ends  of  the  core  of  the  coil  and  the  iron  box,  in  order  to 
make  the  magnetic  lines  jump  a  small  air  gap,  for,  if  the 
magnetic  circuit  were  composed  entirely  of  iron,  the  path 
would  be  so  good  that  the  magnetic  lines  would  keep  on 

36 


37 


Ignition 

spinning  around  in  it  and  would  not  shrink  or  collapse  when 
the  current  is  broken  as  quickly  as  they  should.  The 
proper  amount  of  gap  in  the  magnetic  circuit  is  a  matter 
to  be  carefully  determined. 

Whether  the  coils  are  mounted  in  an  iron  box,  paper  or 
vulcanized  fiber  tube,  they  should  be  filled  in  with  an  insu- 
lating waterproof  wax,  having  a  high-melting  point.  Some 
Make-and-Break  coils  are  insulated  by  winding  a  narrow 
strip  of  paper  around  the  bare  wire,  as  the  latter  is  being 


Types    of    make    and    break    coils. 

wound  on  the  coil,  and,  when  the  winding  is  completed,  the 
coil  is  finished  by  gluing  a  layer  of  paper  around  it.  A  coil 
made  in  this  way  will  give  fairly  good  -results,  provided  it 
is  kept  perfectly  dry  and  free  from  moisture  and  not  con- 
nected with  too  strong  a  battery.  The  only  advantage  in 
this  kind  of  coil  is  that  a  few  cents  can  be  saved  on  the 
cost;  but  this  saving  in  no  way  offsets  the  risk  sustained 
by  its  use. 

GENERAL  FORM  OF  IGNITER. 

The  general  form  of  the  Igniter  can  be  seen  by  the  illus- 
tration. "A"  is  a  cast  iron  member,  carrying  an  insulated 
stationary  electrode,  "B,"  and  a  grounded,  moveable  elec- 
trode "C." 

The  electrode  "B"  must  be  very  carefully  insulated  from 
all  other  parts.  A  built  up  mica  washer,  J^  inch,  or  better, 
•f$  inch  thick,  should  be  used  at  "D."  Irregular  and  weak 
explosions  can  often  be  traced  to  a  faulty  insulation  of  this 

38 


Construction  and  Operation  of  Make-and-Break  Coils 

part.  If  the  mica  washers  become  loose  and  begin  to  sepa- 
rate, dirt  will  get  in  between  them  and  cause  a  partial  short 
circuit.  In  this  event  it  does  little  good  to  tighten  the  old 
washers ;  new,  clean  ones  should  be  substituted. 

Loss  OF  COMPRESSION.  , 

The  moveable  electrode  should  have  a  long,  well  made 
bearing,  or  better,  be  provided  with  a  ground  taper  joint 
on  the  inside  end  in  order  to  prevent  the  escape  of  the  com- 
pressed charge ;  in  fact,  the  whole  igniter  must  be  con- 
structed and  bolted  to  the  cylinder  in  such  manner  as  to  pre- 
vent any  leakage  of  gas.  A  leaky  igniter  is  often  a  cause  of 
poor  compression  and  consequent  loss  of  power. 

The  constant  breaking  of  a  circuit,  with  the  attending 
spark,  has  a  strong  tendency  to  disintegrate  and  burn  the 
contact  surfaces ;  in  fact,  the  current  seems  to  tear  off  ex- 


Make   and   break    ignition   system. 

39 


Ignition 

ceedingly  small  particles  of  the  metal  and  project  them  in  a 
stream  between  the  separating  contacts.  This  provides  a 
fairly  good  conducting  path,  over  which  the  current  con- 
tinues to  flow  for  a  moment,  and,  since  the  current-carrying 
capacity  of  this  stream  of  particles  is  small,  the  current 
heats  it  and  partially  burns  it  up,  as  it  would  a  small  wire. 
The  surrounding  gas  adds  fuel  to  this  burning  stream  of 
particles  and  is  thereby  ignited.  The  metallic  particles  that 
are  not  consumed,  are  either  lost  or  deposited  on  the  nega- 
tive contact.  This  accounts  for  the  "pitting"  of  the  positive 
and  building  up  of  the  negative  contact  points.  For  this 
reason  the  igniter  points  must  be  made  of  some  metal  that 
will  not  readily  disintegrate  and  burn. 

IGNITER  POINTS. 

Platinum  and  iridium  are  the  best  metals  for  this  pur- 
pose. Points  of  pure  platinum,  however,  are  not  quite  hard 
enough  to  withstand  the  mechanical  strain  of  being  con- 
stantly beaten  together,  and  pure  iridium  is  so  hard  and  has 
such  a  high  melting  point  that  it  cannot  be  drawn  into  a 
wire  or  made  into  a  rivet,  but  can  only  be  formed  into 
little  globules  or  spheres,  by  allowing  a  drop  of  the  molten 
metal  to  cool  while  falling.  This  iridium  drop  must  be 
brazed  or  hard-soldered  to  the  contact  arms.  A  rivet  made 
of  an  alloy  of  these  metals,  containing  15  to  20  per  cent  of 
iridium,  is  very  satisfactory,  and  can  easily  be  riveted  to 
the  contact  arms.  A  form  of  hard  nickel  can  be  used  with 
fair  satisfaction  for  the  igniter  points  where  the  mechanical 
wear  and  current  are  not  too  great. 

There  are  several  special  alloys  of  nickel-steel,  etc., 
made  for  this  purpose,  which  are  a  great  deal  cheaper  than 

40 


Construction  and  Operation  of  Make-and-Break  Coils 

platinum   and   iridium,   but  they  are  in  no  way  as  satis- 
factory. 

DURATION  OF  SPARK. 

The  apparent  momentum  of  an  electric  current  is  ex- 
pended in  a  very  short  time  after  the -contact  points  begin 
to  separate ;  that  is,  the  life  of  the  spark  or  arc  in  Make-and- 
Break  ignition  apparatus,  under  working  conditions,  is  ap- 
proximately from  0.0008  to  0.005  second,  as  shown  by  the 
Oscillograph.  This  makes  it  necessary  to  separate  the  con- 
tact points  very  suddenly,  in  order  to  draw  the  arc  out  to 
about  -j^  inch  before  it  dies  out.  To  accomplish  this  sudden 
break,  regardless  of  engine  speed,  a  spring  and  tripping 
mechanism  is  used.  Every  make  of  engine  has  its  own 
particular  design  of  igniter,  but  a  glance  at  any  one,  with 
the  requirements  in  mind,  will  make  it  clear. 

In  order  to  insure  even  and  accurate  timing,  the  tripping 
mechanism  should  be  so  made  that  wear  on  any  of  its  parts, 
as  \vell  as  on  the  igniter  points,  will  not  affect  the  time  the 
spark  occurs.  The  difficulty  of  meeting  this  requirement  is 
one  of  the  main  reasons  why  Make-and-Break  ignition  is 
not  suitable  for  high-speed  multiple-cylinder  motors. 

So  long  as  the  igniter  points  are  in  contact  the  cur- 
rent flows ;  therefore,  to  save  the  battery,  the  contact  should 
be  as  brief  as  possible.  The  circuit  should  be  closed  just 
long  enough  to  allow  the  current  to  build  up  almost  to  its 
maximum,  for  it  is  evident  that  the  spark  will  be  strongest 
if  the  circuit  is  broken  instantly  after  the  current  has 
reached  its  full  strength,  and  will  be  no  stronger  no  matter 
how  long  after  that  the  circuit  is  kept  closed. 

41 


Ignition 

TIME  LENGTH  OF  CONTACT. 

The  time  required  for  the  current  to  build  up  in  Make- 
and-Break  coils,  depends  upon  the  E.  M.  F.  of  the  battery 
and  the  construction  of  the  coil.  With  four  new  dry  cells, 
the  time  required  with  different  makes  of  coils  is  from 
0.015  to  0.10  second.  These  figures  are  not  the  results 
of  theory  or  guess, '  nor  even  of  mathematical  calculation, 
but  are  taken  from  the  record  made  by  the  rising  current 
itself,  in  an  oscillograph,  a  description  of  which  is  given  in 
the  next  chapter. 


Chapter  Six 
The  Oscillograph  and  Tests 

THE  OSCILLOGRAPH. 

In  the  oscillograph,  very  rapidly  changing  electric  cur- 
rents are  made  to  trace  a  permanent  record  of  themselves 
on  a  photographic  film.  Two  thin  strips  of  silver  1/2000 
of  an  inch  thick,  are  suspended  very  close  together  in  a 
strong  magnetic  field,  and  a  tiny  glass  mirror,  0.001  of  an 
inch  thick  and  about  -^  °f  an  incn  square,  is  cemented  to 
the  strips.  A  current  of  electricity  sent  up  one  ribbon  and 
down  the  other  reacts  upon  the  magnetic  field,  tending  to 
push  one  ribbon  forward  and  the  other  backward,  thereby 
slightly  rotating  the  mirror,  the  amount  of  rotation  being  a 
measure  of  the  current  strength.  A  cylinder,  with  a  pho- 
tographic film  wound  around  it,  is  supported  about  twenty 
inches  from  the  silver  strips,  and  a  tiny  beam  of  light  from 
an  arc  lantern  is  focused  on  the  mirror  and  reflected  back 
from  it  through  a  slot  in  a  partition  to  the  cylinder.  The 
whole  is  inclosed  in  a  light-tight  box.  The  cylinder  is  rotated 
at  a  known  speed  and  an  electrically  operated  shutter  allows 
the  beam  of  light  to  strike  the  film  for  one  revolution  only. 
If  the  current  to  be  measured,  or  a  certain  proportion  of  it, 
is  sent  up  and  down  the  strip,  the  mirror  and  beam  of  light 
will  oscillate  according  to  the  variation  of  current.  This 
motion  of  the  spot  of  light,  combined  with  the  rotation  of 
the  film,  wrill  trace  a  curve  on  the  latter.  The  loop  of  silver 

43 


Ignition 

ribbon  with  the  mirror  is  inclosed  in  a  glass  tube,  containing 
the  damping  liquid,  and  is  so  sensitive  that  it  will  respond 
over  6,000  times  a  second. 


The    oscillograph,    a    very    sensitive    instrument    which    makes    an    accurate 
record   of    rapidly   changing    electric    currents    on    a   photographic    film. 

The  oscillograph  the  author  has  in  his  Laboratory  has 
been  specially  arranged  by  him  for  particular  research  work 
along  other  lines,  and  being  extra  sensitive  it  is  peculiarly 
adapted  for  investigating  ignition  apparatus. 

OSCILLOGRAMS  OF   MAKE-AND-BREAK  COILS. 

The  accompanying  "oscillograms"  were  carefully  traced, 
from  the  original  film,  on  squared  paper,  properly  calibrated 

44 


A    series    of    records    taken    from    the    oscillograph,    showing    how    the 

current  builds   up   in   various   coils.      The  current   was   furnished   by 

four  dry  cells   working  through   a   regular   igniter  arranged 

to  make  a  very  long  contact. 

45 


Ignition 

for  time,  from  the  diameter  and  speed  of  rotation  of  the 
film ;  and  amperes,  by  the  deflection  of  the  beam  of  light  by 
a  constant  current  of  known  strength.  They  were  taken 
with  several  different  kinds  of  coils  and  four  dry  cells 
working  through  a  regular  igniter,  the  latter,  however,  for 
convenience,  was  arranged  to  make  a  very  long  contact, 
namely  about  0.1  of  a  second. 

A  thoughtful  study  of  these  curves  will  develop  many 
interesting  facts ;  for  instance,  in  curve  "C-12,"  we  see  that 
the  current  builds  up  to  one  ampere  during  the  first  0.005 
second  and  becomes  1.6  amperes  in  0.01  second,  finally 
reaching  its  maximum  of  2.2  amperes,  as  determined  by 
Ohm's  Law,  after  0.03  second.  The  time  length  of  contact 


o-f  Oscillograph. 


for  this  particular  coil  should  be  between  0.015  and  0.020 
second.  The  current  remains  constant  at  about  2.2  amperes 
until  the  circuit  is  broken,  when  the  arc  begins  and  the  steep 
descent  of  the  curve  indicates  the  current  passing  through 
the  arc.  In  this  instance,  the  arc  lasts  a  little  longer  than 

46 


The  Oscillograph  and  Tests 


0.001  second  and  dies  out  when  the  current,  passing  through 
it,  drops  to  about  1  ampere. 

Curve  "C-ll"  is  taken  from  the  same  coil  as  "C-12," 
excepting  that  the  coil  is  placed  in  an  iron  box.  Note  how 
much  slower  the  current  rises  and  falls.  In  this,  case,  the 
arc  lasts  nearly  0.003  second.  This  type  of  coil  will,  as  a 
rule,  consume  less  current  than  open  core  types,  because  it 
will  permit  a  greater  variation  of  time  length  of  contact 
without  using  too  much  current.  The  time  length  of  con- 
tact for  this  coil  should  be  between  0.02  and  0.04  second. 
Since  the  time  length  of  contact  varies  with  the  speed  of 
the  engine,  and  the  accuracy  with  which  the  igniter  is  made, 
the  advantage  of  an  iron  clad  coil  from  a  standpoint  of 
current  consumption,  is  obvious. 

Curve  "C-13"  was  taken  from  a  coil  not  having  an  iron 
core.  Curve  "C-14"  was  taken  from  the  same  coil  with  an 
iron  core,  showing  the  difference  there  is  between  the 
two.  A  comparison  of  these  curves  proves  the  great  im- 
portance of  the  iron  core. 

E.  M.  F.  OF  SPARK. 

The  momentary  voltage  produced  in  Make-and-Break 
coils  has  to  the  writer's  knowledge  heretofore  been  only 
estimated,  for  it  is  very  difficult  to  make  an  accurate  meas- 
urement, due  to  the  many  conditions  affecting  it.  To  obtain 
an  accurate  measurement  of  this  the  author  constructed  a 
commutator  which  connected  a  special  electrostatic  volt- 
meter across  the  arc  for  about  one  hundred  thousandths  part 
of  a  second.  Various  coils  were  tried,  and  it  was  found 
th;»t  the  momentary  E.  M.  F.  was  from  60  to  200  volts,  de- 
pending upon  the  battery  and  coil. 

47 


Ignition 

Make-and-Break  ignition  is  very  satisfactory  for  single- 
cylinder,  low-speed  engines,  provided  the  igniter  is  properly 
insulated  and  equipped  with  iridium  or  iridium-platinum 
points  and  designed  to  give  a  very  sudden  break,  and  proper 
time  length  of  contact  to  suit  a  well  made  coil.  Most  of  the 
trouble  with  Make-and-Break  ignition  is  in  the  rapid  burn- 
ing and  corroding  of  the  igniter  points,  requiring  frequent 
renewal  and  in  defective  insulation  of  the  stationary  elec- 
trode. Points  of  proper  material,  when  used  with  an 
efficient  coil,  will  last  a  whole  season,  and  often  very  much 
longer. 

Make-and-Break  ignition  may  be  said  to  be  complicated 
mechanically  and  simple  electrically,  and  the  Jump  Spark, 
simple  mechanically,  but  complicated  electrically.  The  ab- 
sence of  levers  and  heavy  moving  parts  makes  the  Jump 
Spark  system  superior  for  high-speed  multiple-cylinder 
engines. 

MAGNETIC  PLUG  SYSTEM. 

A  form  of  Make-and-Break  ignition,  known  as  the 
Magnetic  Plug  system,  has  been  devised  to  meet  the  condi- 
tions in  medium  speed  multiple-cylinder  engines.  In  this 
system,  the  igniter  is  made  very  small  and  light  and  is  oper- 
ated by  an  electro-magnet,  the  whole  being  enclosed  in  a 
metal  shell  not  a  great  deal  larger  than  the  high-tension 
spark  plug,  and  is  screwed  into  the  cylinder  in  the  same 
way.  When  ignition  is  required  an  impulse  of  current  is 
sent  to  the  magnetic  plug,  across  the  igniter  points  through 
the  electro-magnet,  which  then  attracts  its  armature  thereby 
separating  the  contacts. 


48 


Chapter  Seven 
Theory  of  the  Jump  Spark  Coil 

We  have  already  pointed  out  that,  in  order  to  produce 
the  spark  or  arc  in  tnake-and-break  ignition,  it  is  necessary 
that  the  igniter  points  touch  each  other,  then  rapidly  sepa- 
rate. Since  this  involves  considerable  mechanical  action, 
this  system  is  unsuitable  for  high-speed  motors.  In  order 
to  properly  ignite  medium  and  high-speed  engines,  it  is 
necessary  to  eliminate  all  heavy  moving  parts.  This  is 
accomplished  in  the  jump  spark  system,  wherein  the  igniter 
points  are  placed  a  short  distance  apart  and  held  stationary, 
and  the  arc  is  started  between  them  without  previous  con- 
tact. As  stated  in  a  previous  chapter,  this  is  accomplished 
by  increasing  the  E.  M.  F.  sufficiently  to  force  a  current 
against  the  high  resistance  of  the  gas  lying  between  the 
points  of  the  igniter  or  spark  plug,  as  it  is  called  in  this 
case.  The  instant  a  current  starts  to  flow  between  the 
points,  an  arc  is  formed,  very  similar  to  the  arc  in  the  touch 
spark  system,  except  that  the  amperage  or  volume  of  cur- 
rent, passing  through  it,  is  very  much  less.  After  the  arc 
has  been  started,  only  a  few  volts  are  required  to  maintain 
it,  for  the-  resistance  of  the  arc1  itself  is  only  a  few  ohms, 
and,  in  some  cases,  less  even  than  one  ohm. 


1  For  methods  of  measuring  the  resistance  of  arcs  of  various  kinds,  and 
the  E.  M.  F.  required  to  start  them,  see  "The  Principles  of  Electric  Wave 
Telegraphy,"  by  J.  A.  Fleming,  F.  R.  S.,  pages  178  and  152. 

49 


Ignition 

HEAT  OF  SPARK. 

The  heat  of  an  arc  depends  largely  upon  the  amperage 
flowing  through  it.  A  high  voltage  is  needed  only  to  start 
the  arc,  which,  when  started,  should  be  fed  with  considerable 
current.  The  E.  M.  F.  required  to  start  an  arc  depends 
upon  several  conditions,  the  principal  ones  being :  Distance 
between  terminals  or  length  of  spark;  kind  of  surrounding 
gas — its  pressure,  its  temperature ;  nature  and  form  of  ter- 
minals between  which  the  spark  jumps.  We  can  only  briefly 
mention  the  manner  in  which  these  conditions  influence 
spark  potential. 

In  sparks,  from  1-64  inch  to  J4  inch  long,  the  E.  M.  F. 
increases  almost  directly  as  the  length.  The  resistance  of 
various  gaseous  mixtures  used  in  internal  combustion 
motors,  at  atmospheric  pressure,  is  not  very  different  from 
that  of  air. 

SPARK  VOLTAGE. 

The  E.  M.  F.  necessary  to  produce  a  spark  other 
things  being  equal,  varies  almost  directly  as  the  absolute 
pressure.  This  law  is  quite  accurate  up  to  200  pounds  per 
square  inch.  Increasing  the  temperature  of  the  gas  lowers 
the  necessary  voltage.  The  writer  knows  of  no  accurate 
law  expressing  this  relation ;  however,  it  has  been  shown 
that  there  is  no  simple  inverse  law,  as  the  voltage  decreases 
less  rapidly  than  the  temperature  increases.  The  shape  of 
the  terminals  between  which  the  spark  jumps,  influences 
the  necessary  voltage.  For  instance,  much  less  voltage  is 
required  to  produce  a  spark  between  two  sharp  points  or 
from  a  point  to  a  flat  surface  than  between  smooth  surfaces 
or  spheres. 

50 


Theory  of  the  Jump  Spark  Coil 


Many  practical  tests  were  made  to  determine  the  dis- 
tance a  spark  should  jump  in  air  at  atmospheric  pressure, 
to  insure  its  jumping  between  the  points  of  the  spark  plug 
while  igniting  the  engine.  It  was  found  that,  for  compres- 
sions not  exceeding  80  pounds,  a  spark  that  would  jump 
from  fV  inch  to  J4  inch  between  needle  points  in  air,  would 
insure  a  jump  between  the  points  of  a  plug  under  compres- 
sion in  the  cylinder.  Many  persons  have  made  "tests"  on 
coils  and  spark  plugs  by  screwing  the  latter  in  a  box,  in  which 
the  air  was  compressed  to  60  or  80  pounds,  but  these  tests 
are  of  little  value,  unless  the  temperature  of  the  air  is  raised 
to  equal  that  of  the  gases  in  the  cylinder.  It  is  not  easy 
to  determine  the  exact  voltage  necessary  to  produce  this 
spark,  but  it  has  been  shown  that  the  average  jump  spark 
ignition  coil  is  capable  of  producing  a  momentary  open  cir- 
cuit E.  M.  F.  of  from  10,000  to  25,000  volts. 

THEORY  OF  JUMP  SPARK  COIL. 

Let  us  see  how  the  jump  spark  coil  produces  this  enor- 
mous E.  M.  F.  A  jump  spark  coil  consists  essentially  of  an 
iron  core,  around  which  is  wound  a  few  turns  of  rather 
large  wire,  called  the  primary,  and  an  entirely  separate 
winding  of  many  turns  of  fine  wire  called  the  secondary, 
and  some  means  for  making  and  breaking  the  primary  cir- 
cuit. This  is  really  a  make-and-break  coil,  having  two  sepa- 
rate windings.  When  a  current  is  sent  through  the  primary, 
a  magnetic  field  is  formed  around  the  core,  as  we  have  seen, 
and  the  magnetic  lines,  when  expanding  or  collapsing,  cut 
through  the  turns  of  wire  in  the  secondary  winding,  thereby 
producing  in  it  an  E.  M.  F.  The  value  of  this  "induced" 
E.  M.  F.  depends  upon  the  density  of  magnetic  lines,  the 
speed  at  which  they  expand  or  collapse,  and  the  number  of 

51 


Ignition 

turns  of  wire  through  which  they  cut.  The  current,  or  am- 
perage, in  the  secondary  circuit,  depends  upon  the  value  of 
the  induced  E.  M.  F.,  and  the  resistance  of  both  the  sec- 
ondary winding  and  spark  gap. 

It  is  desirable  to  use  as  little  current  as  possible  and 
keep  the  resistance  of  the  secondary  winding  as  low  as  can 
be  done.  Therefore,  in  order  to  produce  the  necessary 
E.  M.  F.  with  a  limited  number  of  both  magnetic  lines  and 
turns  of  wire  in  the  secondary,  the  magnetic  lines  must  be 
made  to  collapse  as  quickly  as  possible. 

We  have  seen  that  the  arc,  which  forms  when  the  pri- 
mary circuit  is  broken,  allows  the  current  and  consequently 
the  magnetic  field,  to  die  down  rather  slowly.  If  this  arc 
were  prevented,  the  current  would  suddenly  be  stopped  and 


Diagram   showing   action   of   the   jump   spark   coil. 


a  very  rapid  collapse  of  the  magnetic  lines  would  follow. 
While  there  are  several  ways  for  preventing  the  arc,  such 
as  directing  a  blast  of  air  against  it,  or  placing  it  in  a  strong 
magnetic  field,  the  best  method  is  to  absorb,  in  a  condenser, 

52 


Theory  of  the  Jump  Spark  Coil 


the   momentary   "extra"   current,   which  would  otherwise 
form  the  arc. 

THEORY  OF  CONDENSER. 

A  condenser  consists  essentially  of  two  thin,  metal 
strips,  of  considerable  area,  placed  a  short  distance  apart, 
but  carefully  insulated  from  each  other.  If  these  metal 
strips  are  connected  respectively  to  the  contact  points,  be- 
tween which  the  primary  circuit  is  broken,  the  "extra"  cur- 
rent, which  would  otherwise  form  the  arc,  finds  it  easier 
to  rush  on  to  the  strips  and  spread  itself  over  their  sur- 
face, thereby  charging  them  with  static  electricity.  After 
the  magnetism  has  subsided,  the  condenser  discharges 
through  the  primary  winding,  and  is  then  ready  to  receive 
the  sudden  rush  of  current  at  the  next  break.  As  a  matter 
of  fact,  however,  the  discharge  of  the  condenser  has  a  slight 
tendency  to  cause  a  more  complete  collapse  of  the  magnetic 
lines,  thereby  slightly  increasing  the  E.  M.  F.  in  the  sec- 
ondary. While  it  is  impracticable  to  entirely  eliminate  the 
spark  at  the  contact  points  it  can  be  so  far  lessened  as  to 
reduce  the  wear  on  them  to  a  minimum.  The  contact  points 
in  this  case,  as  in  the  make-and-break  system,  must  be  made 
of  iridium-platinum. 

The  secondary  winding  must  have  several  thousand 
turns,  therefore  a  very  small  wire  must  be  used.  The  tre- 
mendous voltage  produced  demands  a  very  careful  insula- 
tion and  arrangement  of  the  turns.  The  secondary  winding 
is,  perhaps,  the  most  important  part  of  the  coil. 

THEORY  OF  VIBRATOR. 

In  order  to  produce  a  stream  of  sparks,  the  primary 
circuit  must  be  rapidly  made  and  broken.  In  the  vibrating 

53 


Ignition 

type  of  coil,  this  is  accomplished  by  supporting  a  thin  piece 
of  iron,  having  a  contact  point  on  it,  near  one  end  of  the 
core.  The  current,  from  the  battery,  on  its  way  to  the 
primary  winding,  is  made  to  pass  through  a  stationary  con- 
tact point,  into  the  point  on  the  iron  head.  When  the  core 
becomes  magnetized  the  iron  head  is  attracted ;  the  circuit  is 
thus  broken,  and  the  core  loses  its  magnetism,  allowing  the 
vibrator  to  spring  back  into  contact  again.  This  process  is 
repeated  several  hundred  times  a  second.  Since  the  vibrator 
is  operated  automatically  by  the  magnetic  attraction  of  the 
core  whenever  a  current  is  sent  through  the  primary,  means 
must  be  provided  for  closing  the  primary  circuit  at  the 
instant  ignition  is  required.  This  is  accomplished  by  the 
use  of  a  contact  maker,  called  the  timer  or  commutator, 
which  is  operated  by  the  cam  shaft  of  the  engine. 

Having  now  a  general  idea  of  the  theory  of  a  jump 
spark  coil,  let  us  follow  it  through  a  complete  cycle. 

COMPLETE  ACTION  OF  COIL. 

Contact  having  been  made  at  the  timer,  the  current 
from  the  battery  starts  flowing  across  the  points  on  the 
vibrator  through  the  primary  winding,  where  it  circulates 
around  the  iron  core,  then  back  to  the  battery.  The  instant 
the  current  starts,  it  begins  to  magnetize  the  space  around 
it,  which  effect  is  greatly  concentrated  in  the  primary  in  the 
manner  already  described.  As  the  magnetic  field  is  expand- 
ing, the  lines  of  force  cut  through  the  many  turns  of  sec- 
ondary winding,  thereby  producing  in  it  an  E.  M.  F.  which, 
owing  to  the  comparatively  low  rate  of  expansion,  is  too 
feeble  to  force  a  current  across  even  a  very  small  air  gap. 
When  the  magnetic  field  has  grown  strong  enough  to  attract 
the  vibrator  armature  against  the  tension  of  its  spring,  the 

54 


Theory  of  the  Jump  Spark  Coil 


circuit  is  broken,  and  the  "extra"  current  which  would  other- 
wise maintain  itself  for  an  instant  by  arcing  between  the 
points,  is  absorbed  by  the  condenser  and  thus  suddenly 
choked  off.  The  magnetic  lines  accordingly  shrink  very 
rapidly,  cutting  through  the  secondary  turns  with  sufficient 
speed  to  cause  a  considerable  E.  M.  F.  strong  enough  this 
time  to  overcome  the  resistance  of  an  air  gap  and  force  a 
current  across  it  in  the  form  of  the  familiar  jump  spark. 
This  spark  lasts  only  until  the  energy  of  the  shrinking  lines 
is  expended,  when  the  vibrator  is  no  longer  attracted  by  the 
core  and  it  springs  back  into  contact  again.  The  whole 
process  is  repeated  with  surprising  rapidity. 


55 


Chapter  Eight 

Practical    Construction    and    Oper- 
ation of  the  Jump  Spark  Coil* 

Having  in  the  last  chapter  described  the  theory  of  the 
Jump  Spark  Coil,  the  manner  of  its  practical  construction 
will  now  be  given. 

THE  PRIMARY. 

The  core  consists  of  a  number  of  soft  Norway  iron 
wires,  Nos.  20  or  22  gage,  packed  tightly  into  a  card  board 
tube  from  4  to  8  inches  long,  and  ^  to  J4  incn  m  diameter. 
Around  this  are  usually  wound  two  layers  of  insulated  cop- 
per wire,  varying  in  size,  according  to  conditions,  from  No. 
16  to  No.  20  gage.  It  is  important  that  the  iron  wires  be 
thoroughly  annealed  to  make  them  as  soft  as  possible,  and 
also  to  give  them  a  coat  of  scale  which  tends  to  insulate  them 
one  from  another,  thereby  preventing  a  loss  of  energy 
through  the  production  of  Foucault  or  Eddy  currents.  A 
turn  of  oiled  paper  or  cloth  should  be  placed  between  the 
layers  of  wire,  and  it  is  well  to  dip  the  whole  primary  in 
paraffine,  or  better,  an  insulating  compound  having  a  higher 
melting  point. 

THE  VIBRATOR. 

The  vibrator  is,  perhaps,  the  most  troublesome  part  of 
the  coil  to  correctly  design,  consequently  there  are  many 
different  forms  on  the  market.  Since  no  fixed  rule  can  be 

*(For    a    treatise    on    the    practical    construction    of   coils,    see    ''Induction 
Coils,"   by  A.   Frederick   Collins.) 

56 


a.  1 


IB 


Ignition 

laid  down  for  its  construction,  we  will  briefly  mention  a  few 
things  that  go  to  make  up  a  good  vibrator. 

In  the  first  place,  it  should  be  very  simple  and  free  from 
delicate  adjustments,  particularly  if  it  is  to  be  used  by  a 
novice,  as  is  usually  the  case.  It  is  considered  good  practice 
by  many  manufacturers  to  have  both  contact  points  station- 
ary and  effect  the  adjustment  by  regulating  the  tension  of 
the  spring  supporting  the  soft  iron  head.  This  permits  a 
uniform  distance  between  the  core  and  vibrator  at  all  times, 
and  also  increases  the  life  of  the  contact  points,  for,  after 
they  have  become  worn  to  fit  each  other,  their  relation  is  not 
disturbed  by  adjustment  as  would  be  the  case  if  one  point 
were  mounted  on  an  adjusting  screw.  Good  sized  points, 
made  of  the  best  grade  of  iridium-platinum,  should  be  used 
for  the  contacts. 

Some  vibrators,  known  as  "Hammer  Break,"  have  one 
platinum  point,  mounted  on  a  spring  separate  from  the  iron 
head.  A  hook  or  catch,  mounted  on  the  latter,  after  it  has 
begun  to  move,  strikes  this  spring,  effecting  a  very  sudden 
and  positive  separation  of  the  contacts.  While  this  tends  to 
give  a  slightly  longer  spark,  it  is  more  complicated,  and,  as 
a  rule,  not  quite  as  responsive  or  rapid  as  some  other  styles, 
and  also  generally  consumes  more  current. 

It  is  well  to, have  the  adjustment  so  designed  as  to  pre- 
vent the  possibility  of  "freezing"  the  vibrator ;  viz.,  bringing 
the  contacts  together  so  tightly  that  they  cannot  vibrate, 
thereby  rendering  the  coil  inoperative  and  causing  an  ex- 
cessive waste  of  current.  As  a  rule,  the  current  consump- 
tion is  lessened  by  placing  the  vibrator  closer  to  the  core, 
and  particularly  by  reducing  the  pressure  between  the  con- 
tact points;  this,  of  course,  also  reduces  the  strength  of 

58 


Practical  Construction  and  Operation  of  the  Jump  Spark  Coil 

spark.  Therefore,  to  adjust  a  vibrator  to  be  economical  in 
current,  reduce  the  pressure  between  the  points  as  much  as 
possible,  without  causing  the  engine  to  miss  fire. 

THE  CONDENSER. 

There  are  several  ways  for  making  a  condenser,  but 
only  one  of  the  best  will  be  mentioned. 

Two  strips  of  very  thin  tin  foil,  separated  by  a  double 
thickness  of  special  paper,  are  wound  into  a  compact  roll, 
then  soaked  for  several  hours  in  hot  wax.  After  the  paper 
is  thoroughly  impregnated,  the  condenser  is  placed  under  a 
pressure  of  several  tons,  which  squeezes  out  all  surplus 


Condenser    shown    on    the    left — before    soaking   in    wax. 

Finished   condenser   on   the    right,   after   it   has 

been    impregnated    and    subjected    to 

several   tons   pressure. 

59 


Ignition 

wax,  and,  after  cooling,  it  is  as  compact  as  a  board.  This 
does  away  with  troublesome  air  spaces  between  the  layers 
of  paper  and  foil,  and  insures  a  minimum  and  uniform  dis- 
tance between  the  tin  foil  sheets.  The  importance  of  this  is 
apparent  when  we  remember  that  the  capacity  of  a  con- 
denser, other  things  being  equal,  varies  inversely  as  the  dis- 
tance between  the  tin  foil  sheets.  It  is  also  desirable  for 
the  condensers  to  be  of  uniform  capacity.  The  connecting 
wires  are  soldered  respectively  to  the  folded  edges  of  the 
two  tin  foil  strips,  as  the  photograph  shows. 

As  the  condenser  of  an  ignition  coil  is  subjected  to  sud- 
den surgings  of  potential  reaching  several  hundred  volts, 
the  insulation  between  the  tin  foil  strips  must  be  very  good 
to  prevent  a  breakdown.  The  actual  capacity  of  con- 
densers used  in  various  ignition  coils,  is  from  0.1  to  0.4 
Microfarad. 

SECONDARY  WINDING. 

When  it  is  realized  that  a  current  under  a  pressure  of 
10,000  to  20,000  volts  is  produced  and  made  to  circulate 
many  times  in  the  secondary  of  an  ignition  coil,  it  is  needless 
to  say  that  the  most  careful  arrangement  and  insulation 
of  the  turns  are  necessary.  The  conventional  method  of 
making  the  secondary  consists  in  winding  a  fine  insulated 
wire  in  even  layers  around  a  paper  tube,  just  large  enough 
to  slip  over  the  primary,  the  layers  of  wire  being  separated 
one  from  another  by  one  or  two  turns  of  thin  paper.  When 
the  required  number  of  layers  are  wound,  which  is  usually 
between  30  and  50,  the  coil  is  soaked  for  several  hours  in 
melted  wax.  In  order  to  insure  thorough  and  uniform 
insulation,  it  is  best  to  use  the  vacuum  impregnating  process, 

60 


Practical  Construction  and  Operation  of  the  Jump  Spark  Coil 


A   group  of  secondary  windings.     The  three  on  the  left  are   wound 

by  the   Pancake   system.      The   small  winding  in  the   foreground 

is  taken  from  a  very  cheap  coil.     A  pile  of  iron  core  wires 

with    a    finished    primary    are    shown    on    the    right. 

which  consists  essentially  of  thoroughly  drying  the  winding 
in  an  oven  in  which  a  partial  vacuum  is  created.  The 
melted  wax  is  then  allowed  to  flow  into  the  oven  under 
pressure.  This  helps  to  force  the  insulating  compound 
into  the  center  of  the  winding,  and  also  drives  out  all  trace 
of  moisture.  Where  the  layer  method  of  winding  is  used, 
it  is  almost  necessary  to  employ  the  vacuum  process  to  se- 
cure satisfactory  insulation.  In  order  to  lessen  the  danger 
of  a  breakdown  or  "burnout"  of  the  secondary,  it  is  usually 
wound  in  two  separate  parts,  which  are  connected  in  series. 
To  prevent  a  spark  passing  from  one  section  to  the  other,  a 
space  is  left  between  them  which  is  filled  with  wax. 

"PANCAKE"  WINDING. 

There  is  a  patented  method  of  winding,  in  which  the 
secondary  is  wound  in  10  to  16  little  rubber  spools  or  sec- 
tions, which  are  slipped  over  the  primary  and  connected  in 
series.  The  wire  used  has  a  special  cotton  covering.  The 
spools  are  actually  wound  in  a  bath  of  melted  wax,  which 
is  constantly  kept  at  a  temperature  just  above  the  boil- 

61 


Ignition 


rass  Packinct. 


G-rcutfd 
E lectrode . 


Showing  general  scheme  of 
high    tension   spark   plug. 


ing  point  of  water.  This  insures  the  complete  saturation 
of  every  inch  of  wire  and  also  makes  air  spaces  and  moisture 
within  the  winding  impossible.  In  this  construction,  known 


Steel 
Keller 


White 
Fibre. 


Timer    for   vibrating    coil    (4-cyl.). 

62 


Practical  Construction  and  Operation  of  the  Jump  Spark  Coil 

as  the  "pancake  method/'  the  insulation  runs  at  right  angles 
to  the  core,  making  the  difference  of  potential  increase  with 
the  length  of  the  winding,  instead  of  its  height,  which  latter 
is  the  case  in  the  layer  method,  where  the  insulation  runs 
parallel  to  the  core.  In  the  layer  winding,  the  maximum 
difference  of  potential  exists  between  the  top  and  bottom 
layers,  which  are  not  often  separated  more  than  %  inch, 
and,  if  there  is  a  flaw  in  the  insulation,  particularly  at  the 
ends,  a  breakdown  may  occur.  This,  however,  does  not  often 
happen  in  a  modern  well  made  vacuum  impregnated  coil. 
In  the  "pancake"  winding,  the  greatest  difference  of  poten- 
tial is  between  the  two  ends  of  the  winding,  which  are  from 
3  to  5  inches  apart.  A  breakdown  in  this  winding  is  prac- 
tically impossible. 

There  are  several  other  advantages  to  be  gained  by 
the  "pancake  method"  of  winding ;  among  others,  the  elimi- 
nation of  electrostatic  capacity  and  self-induction  of  the 
winding  which  tends  to  produce  a  very  responsive  and  quick 
acting  coil.* 

The  secondary  windings  of  ignition  coils  contain  from 
8,000  to  25,000  turns,  depending  upon  the  make  of  coil. 
The  size  of  wire  used  is  between  No.  34  and  No.  38  B.  &.S. 
gage. 

BALANCE  OF  PARTS. 

All  parts  of  a  coil  must  be  carefully  designed  to  work 
well  together.  For  instance:  If  the  condenser  is  too  small 
or  sluggish  in  action,  the  contact  points  will  often  flash  and 
quickly  burn,  and,  on  the  other  hand,  if  it  is  too  large,  the 
secondary  spark  will  be  shortened  and  tend  to  hesitate  be- 

*See   "Induction    Coils,"    by   Armagnat,   pp.    41,   44   and    78. 

63 


Ignition 

fore  jumping,  particularly  if  made  to  pass  between  round, 
smooth  surfaces.  The  size  and  number  of  turns  of  wire  on 
the  primary  is  determined  largely  by  the  quickness  and  re- 
sponsiveness of  the  vibrator.  Many  other  things  have  to 
be  worked  out,  for  it  is  not  a  simple  matter  to  correctly  de- 
sign a  coil. 

After  the  coil  and  condenser  are  assembled  in  a  box 
or  hard  fiber  tube,  the  latter  should  be  filled  with  a  good  in- 
sulating waterproof  compound  that  will  not  melt  in  hot 
weather  or  if  installed  in  a  hot  place. 


64 


Chapter  Nine 
Oscillograph  Tests  of  Vibrating  Coils 

It  is  well  known  that  an  ammeter,  connected  in  series 
with  a  vibrating  coil  and  battery,  will  indicate  from  %  to  1 
or  more  amperes.  Since  the  vibrator  is  constantly  interrupt- 
ing the  current,  it  is  evident  that  the  current  passing  through 
the  coil  is  not  steady,  but  is  a  series  of  separate  impulses, 
and  that  the  ammeter  simply  indicates  their  average  value.1 
The  oscillograph2  is  the  only  instrument  that  is  quick  and 
sensitive  enough  to  accurately  record  the  current  impulses. 
The  accompanying  oscillograph  tests  were  made  on  several 
well  known  makes  of  coils,  operated  by  a  regular  roller  timer 
and  storage  battery.  Each  group  of  lines  indicates  one  con- 
tact at  the  timer,  and  each  line  shows  the  current  used  each 
time  the  vibrator  breaks  the  circuit.  A  careful  study  of 
these  records  will  develop  many  interesting  facts.  For 
lack  of  space,  brief  mention  only  of  a  few  of  the  most 
important  will  be  made. 

The  first  thing  noticed  is  the  fact  that,  in  some  cases 
nearly  five  amperes  are  required  to  operate  the  vibrator ;  in 
other  words,  a  series  of  current  impulses,  each  reaching  a 
maximum  of  2  to  5  amperes,  is  needed  to  operate  a  vibrating 
coil.  This  explains  why  a  battery  will  not  work  after  its 


1  This  reading  may  not  be  the  same  with  all  types  of  moving  coil  am- 
meters. A  hot  wire  ammeter  will  give  the  root  mean  square  (square  root 
of  the  average  square). 

2See    Chapter    Six,    page    43. 

65 


Ignition 


amperage  is  reduced  below  a  certain  limit,  and  also  that 
comparatively  large  wires,  namely  No.  12  or  No.  14  gage, 
should  be  used  to  make  the  connections,  and  still  larger 
wires  if  the  battery  is  placed  more  than  a  few  feet  from 
the  coil. 

It  also  will  be  noticed  that  in  some  coils  the  first  im- 
pulse of  the  vibrator  requires  more  current  than  the  suc- 
ceeding ones,  and  in  others  less  current  is  required.  The 
vibrator  breaks  the  circuit  several  times  during  one  contact 


s  .0        .01       .02        .03      ,04-      .05       .06       -07      .08       .09       JO       .11        ./2      .13 

Seco  n  ds. 

Oscillograph    records    of    the    current    in    the  primary  circuit  of  various 
vibrating  coils. 

66 


Oscillograph  Tests  of  Vibrating  Coils 


at  the  timer,  causing  as  many  separate  sparks  at  the  plug. 
If  the  first  spark,  which  occurs  the  first  time  the  vibrator 
breaks  the  circuit  after  contact  is  made  at  the  timer,  is  too 
weak  to  ignite  the  charge,  ignition  will  be  delayed  until  the 
second  or  third  interruption  occurs.  This  partly  accounts  for 
the  so-called  "lag"  in  some  kinds  of  coils.  Curve  "B  2" 
illustrates  this  kind  of  a  vibrator.  Curve  "B  3",  on  the 
other  hand,  is  from  a  coil  that  takes  more  current  for  the 
first  impulse  of  the  vibrator  than  the  succeeding  ones ;  con- 


a 


0        .Ol         .02       .03         -O-f       .05       ,O6       .07       .08 

Secon  ds. 


IQ         II          .12 


Oscillograph  records  of  the    current    in    the    primary    circuit    of    various 
vibrating  coils. 

67 


Fio.3 


Contact    Breaker    for    non-vibrating 
coil,    which    cannot    stop    on    con- 
tact    and     gives     a     uniform 
length    of    contact    at    all 
speeds. 

68 


Oscillograph  Tests  of  Vibrating  Coils 


sequently  the  spark,  resulting  from  this  first  impulse,  will 
be  stronger  than  the  following  ones,  and  will  invariably  ig- 
nite the  charge.  In  this  case  the  several  following  sparks  do 
no  good  and  it  will  also  be  noticed  that  the  current  required 
for  these  extra  sparks  is  comparatively  small.  This  type 
of  coil  has  very  little  "lag,"  and  is,  therefore,  particularly 
good  for  high-speed  motors.  It  will  not  work,  however, 
quite  as  well  on  an  old  battery  low  in  amperage  as  the  other 
type  (B  2),  unless  a  multiple  battery  is  used.  Curve  "B  6" 
represents  the  very  irregular  action  of  a  poorly  designed 
vibrator  working  on  an  improperly  balanced  coil. 

NoN-VlBEATING  JlJMP    SPARK   CoiLS. 

A  mechanical  circuit  breaker  is  often  substituted  for  the 
vibrator,  and  geared  to  the  engine,  so  as  to  break  the  circuit 
the  instant  ignition  is  required.  In  this  system  only  one 
spark  occurs  at  the  plug,  but,  if  it  is  strong  enough,  it  is  all 
that  is  needed.  Fig.  6  illustrates  this  type  of  timer,  as  used 


Platinum  TWAs. 


036"Thic/< 

Si-eel  Burton. 


Case  Hardened. 

End   of  Half- 
Time 


Fig.   6.     Timer  for  non-vibrating  coil. 

on  motorcycles  and  many  types  of  small  stationary  engines. 
The  fact  that  this  timer  can  stop  with  the  points  in  con- 
tact is  an  objection,  because  when  this  happens,  the  battery 

69 


Ignition 

is  rapidly  used  up.  Figs.  1,  2  and  3  clearly  show  a  contact 
breaker  which  can  never  stop  with  the  points  together.  The 
time  length  of  contact,  and  therefore  the  strength  of  spark, 
is  the  same  at  all  engine  speeds.  This  apparatus  uses  very 
little  current. 


70 


Chapter  Ten 
Dynamic  Electricity 

How  AN  ELECTRIC  CURRENT  is  PRODUCED  BY  MECHANICAL 
MEANS  IN  DYNAMOS  AND  MAGNETOS. 

In  the  Introductory  it  was  stated  that  there  are  two 
principal  methods  for  producing  an  electric  current,  viz. : 
Galvanic  or  chemical,  and  Dynamic  or  mechanical.  Con- 
sider now  how  an  electric  current  can  be  produced  by 
mechanical  means. 

As  already  mentioned,  electricity  and  magnetism  are 
very  closely  related.  An  electric  current  magnetizes  the 
space  around  it ;  in  other  words,  an  electric  current  produces 
magnetism.  This  process  can  be  reversed  and  magnetism 
made  to  produce  an  electric  current.  It  is  well  right  here  to 
call  attention  briefly  to  a  few  facts  concerning  magnetism, 
and  clearly  fix  in  mind  just  what  is  meant  by  the  phrase 
"magnetic  lines  of  force. " 

MAGNETISM. 

There  is  no  known  insulator  of  magnetism.  It  passes 
quite  freely  through  the  air,  and,  with  practically  equal  free- 
dom, through  all  other  substances,  with  the  exception  of 
iron — and  its  various  modifications — nickel  and  cobalt. 
These  latter  metals  offer  a  better  path  than  air.  Iron,  being 
the  best,  will,  according  to  its  chemical  and  physical  proper- 
ties, conduct  magnetism  from  100  to  about  10,000  times  bet- 
ter than  air.  Magnetism,  like  electricity,  can  flow  only  in 

71 


Sparks    from    a    30-inch    induction    coil    playing    around    a    glass    plate    five 

feet    square — an     artificial     thunder    and    lightning    storm,    making 

a    noise    like    a    broadside    of    gattling    guns. 

72 


Dynamic  Electricity 


closed  circuits.  Every  magnetic  line  of  force  is  assumed  to 
pass  out  -from  the  north  (  +  )  pole,  and  make  a  complete 
circuit  through  the  surrounding  medium  and  return  into 
the  south  ( — )  pole,  then  through  the  magnet  to  the  north 
pole  again,  and  so  on.  The  path  through  which  the  lines 


Diagram   showing  the   path    or   circuit   taken   by   the   magnetic 
lines  of  force  around  a  bar  magnet. 

of  force  travel,  is  called  the  magnetic  circuit,  and,  like  an 
electric  current,  the  amount  of  magnetism  that  will  flow, 
other  things  being  equal,  depends  upon  the  resistance  or 
reluctance,  as  it  is  called,  of  the  magnetic  circuit.  The 
region  near  the  poles  of  a  magnet,  traversed  by  lines  of 
force,  is  spoken  of  as  a  magnetic  field.  The  directions  taken 
by  the  lines  of  force  can  be  shown  by  placing  a  small  com- 
pass in  the  magnetic  field.  The  needle  will  swing  around  so 
as  to  be  parallel  (or  tangent)  to  the  lines  of  force,  and  its 
north  pole  will  point  in  the  direction  of  the  magnetic  lines. 

73 


Ignition 


Diagram    showing    the    induced    current    and    the    direction    it   takes   in    a    wire, 

as  the  latter  is  being  moved   across  a  magnetic   field   in   the   direction 

shown   by   the   arrow.      The   compass   needle    will   turn   in   the 

direction  indicated. 

MAGNETIC  STRENGTH. 

In  order  to  compare  magnetic  fields  of  different 
strengths,  the  following  unit  was  adopted :  The  unit  mag- 
netic pole  is  a  pole  of  such  strength  as  will  repel  a  similar 
pole  of  equal  strength  ivhen  placed  in  air,  one  centimeter 
away,  with  a  force  of  one  dyne.  Imagine  a  magnetic  pole 
of  unit  strength,  placed  in  the  center  of  a  sphere  having  a 
radius  of  one  centimeter;  a  certain  quantity  of  magnetism 
will  pass  through  every  square  centimeter  of  the  surface  of 
the  sphere.  This  particular  amount  has  been  adopted  as  the 
unit  quantity  of  magnetism,  and  is  known  as  one  line  of 
force.  The  name  "Maxzveli"  after  J.  Clerk  Maxwell — the 
first  great  mathematical  electrician — is  often  substituted  for 
the  phrase  "line  of  force,"  and  so  a  magnetic  field,  through 
which  20  lines  of  force  pass,  may  be  said  to  have  a  strength 
of  20  maxwells.  Since  the  surface  area  of  a  sphere  of 
radius  "r"  equals  47rr2,  the  area  of  a  sphere  having  a  radius 
of  one  centimeter  is  12,57  square  centimeters.  From  this  it 

74 


Dynamic  Electricity 


follows  that  every  magnetic  pole  of  unit  strength  sends  out 
12.57  lines  of  force  or  maxwells. 

MAGNETIC  DENSITY. 

The  unit  of  magnetic  or  "flux"  density  is  called  a  gauss, 
and  is  that  density  resulting  when  one  maxwell  passes  at 
right  angles  through  an  area  of  one  square  centimeter;  hence 
a  magnetic  field  may  be  spoken  of  as  having  a  flux  density 
of,  say  5,000  gausses,  meaning  that  5,000  maxwells  pass, 
at  right  angles,  through  every  square  centimeter. 

In  the  light  of  the  above  facts,  the  following  statement 
of  the  fundamental  principle  of  dynamo  electric  generators 
will  be  readily  understood :  Whenever  a  conductor  and  mag- 
netic lines  of  force  are  made  to  intersect  one  another,  an 
E.  M.  F.  is  produced  in  that  conductor,  and,  if  its  ends  are 
connected,  thereby  completing  the  circuit,  an  electric  current 
will  How.  This  phenomenon  can  easily  be  illustrated  by 
passing  between  the  poles  of  an  ordinary  horseshoe  magnet, 
a  wire  having  a  galvanometer  included  in  its  circuit.  If  a 
galvanometer  is  not  handy,  make  one  by  winding  a  few  turns 
of  insulated  wire  around  a  pocket  compass,  as  shown  in 
Fig.  2.  Note  that  the  compass  needle  will  swing  in  one 
direction  when  the  wire  is  entered  between  the  poles  of  the 
magnet,  and  in  the  opposite  direction  when  it  is  zvithdrawn. 
This  shows  that  the  direction  taken  by  the  so-called  "in- 
duced" current  depends  upon  the  relative  direction  of  mo- 
tion of  the  wire  through  the  magnetic  field. 

The  value  of  the  E.  M.  F.  so  produced,  depends  directly 
upon  the  three  following  conditions :  The  density  of  mag- 
netic flux,  through  which  the  wire  passes;  the  length  of 
"active"  wire — that  part  of  the  wire  that  actually  cuts 
through  the  magnetic  flux;  and  the  speed  with  which  the 

75 


Ignition 

wire  is  passed  across  the  magnetic  field.  The  current  or 
amperage  depends,  as  we  already  know  by  Ohm's  Law, 
directly  upon  the  E.  M.  F.  and  inversely  upon  the  resistance 
of  the  circuit. 

Fig.  3  illustrates  the  principles  of  a  direct-current  elec- 
tric generator.  The  magnetic  field  is  furnished,  in  this  case, 
by  a  permanent  magnet.  The  wire  which  cuts  through  the 
lines  of  force  is  a  single  turn,  rectangular  in  shape,  and 
mounted  on  a  shaft.  When  the  latter  is  rotated  in  the  direc- 


Ficj.3. 

Diagrammatic    view     of    simple    generator,     showing,     respectively,     the 

direction  of  rotation,  magnetic  lines  of  force, 

and    induced   current. 

76 


Dynamic  Electricity 


tion  indicated  by  the  arrows,  both  long  sides  of  the  winding 
will  cut  through  the  lines  of  force  in  such  manner  as  to 
cause  a  current  to  flow  in  the  direction  shown  by  the  arrows. 
In  Fig.  3,  the  armature  is  in  the  most  advantageous  position, 
that  is,  the  maximum  number  of  lines  of  force  are  being 
cut,  and,  consequently,  the  current  is  at  its  maximum.  As 
the  armature  continues  to  rotate,  the  number  of  lines  of 
force  being  cut  becomes  gradually  less  and  less,  until,  after 
revolving  a  quarter  of  a  turn  the  position  shown  in  Fig.  4 
is  reached  where  no  lines  of  force  are  being  cut  and  the 
current  accordingly  has  dropped  to  zero.  As  rotation  con- 
tinues, the  winding  begins  again  to  cut  the  lines  of  force, 


Ficj.4. 

Same  as  Fig.   3,   except  armature  has   advanced  90   degrees  and  is  NOT~ 

cutting   any  lines   of   force,    therefore   no 

current  is  produced. 


Ignition 

reaching  a  maximum  at  the  next  quarter  revolution,  when 
the  current  is  once  more  strongest.  In  this  manner,  the 
current  fluctuates  between  maximum  and  zero  values,  two 
impulses  of  current  being  produced  every  revolution. 

COLLECTING  BRUSHES. 

The  current  from  the  armature  winding  is  collected  by 
means  of  two  copper  brushes,  bearing  against  a  split  copper 
ring,  each  half  of  which  is  connected  to  an  end  of  the 
armature  winding.  Observe  that,  as  the  armature  revolves, 
the  current  produced  in  the  winding  reverses  its  direction 
twice  in  a  revolution.  In  order  to  make  the  current,  taken 
away  from  the  machine  by  way  of  the  brushes,  flow  in  one 
direction,  it  becomes  necessary  to  reverse  the  connections 
between  the  armature  winding  and  the  brushes  twice  in 
every  revolution.  This  is  precisely  what  takes  place  as  the 
brushes  slide  from  one  copper  segment  to  the  other  during 
rotation. 

COMMUTATOR. 

These  copper  segments  are  called  the  commutator  and 
serve  the  double  purpose  of  leading  the  current  away  from 
the  armature  winding  and  making  it  uni-directional. 

A  current  constantly  fluctuating  in  strength  is  not,  as  a 
rule,  as  desirable  as  if  it  were  of  uniform  value.  If  several 
coils,  instead  of  one,  are  wound  on  the  armature  and  their 
ends  properly  connected  to  a  commutator,  having  as  many 
segments  as  there  are  coils,  the  current  will  be  quite  uni- 
form in  strength ;  since,  no  matter  in  what  position  the 
armature  may  happen  to  be,  a  few  of  the  coils  will  always 
be  cutting  the  lines  of  force.  The  greater  the  number  of 
coils  there  are,  the  more  steady  will  be  the  current. 

78 


Dynamic  Electricity 


MAGNETIC  CIRCUIT: 

We  have  already  seen  that  the  value  of  the  induced 
E.  M.  F.  depends  among  other  things  upon  the  strength  of 
the  magnetic  field.  In  order  to  make  the  magnetic  field  as 
strong  as  possible,  the  reluctance  of  the  magnetic  circuit 
must  be  reduced  to  a  minimum.  Obviously,  most  of  the 
reluctance  of  the  circuit  is  in  the  air  gap  between  the  pole 
pieces.  If  this  air  gap  were  filled  with  soft  iron,  the  reluct- 
ance would  be  very  greatly  reduced,  and  the  magnetic 
density  thereby  increased  many  times.  The  only  way  this 
can  be  accomplished,  for  obvious  reasons,  is  by  winding  the 
coil  around  an  iron  cylinder  or  drum,  and  allowing  it  to 
rotate  with  the  armature.  The  drum,  or  armature  core,  is 
made  to  fit  the  pole  pieces,  allowing  only  the  necessary 
clearance,  and  the  winding  is  placed  in  grooves,  parallel  to 
the  axis  of  rotation.  In  order  to  prevent  so-called  Eddy 


Fig.    5 — Photograph    of    a    "drum"    wound    armature,    showing 

commutator    and    several    coils,    and    two    types 

of   soft   iron   armature   discs. 

currents  from  being  produced  and  circulating  around  in  the 
iron  core,  the  latter  is  usually  built  up  of  many  thin,  soft 
iron  discs,  coated  with  varnish,  to  insulate  them  one  from 
another. 

79 


Ignition 

ARMATURE. 

The  accompanying  photograph  shows  a  finished  "drum" 
armature,  taken  from  a  small  six-volt  dynamo.  The  greater 
the  number  of  turns  of  wire  in  each  coil  of  the  armature  the 
higher  will  be  the  voltage.  In  small,  low-tension  machines 
for  ignition  service,  giving  four  to  ten  volts,  there  may  be 
anywhere  from  10  to  50  turns  in  each  coil.  Of  course, 
the  voltage  increases  with  the  speed  of  rotation.  There  are 
a  few  other  ways  for  winding  an  armature,  but  the  princi- 
ples involved  are  exactly  the  same.  The  drum  armature, 
however,  is  the  most  popular.  If  some  one  could  design  a 
generator  that  would  give  a  uniform  voltage,  regardless  of 
speed,  and  without  complicated  governors,  etc.,  a  long-felt 
want  in  the  ignition  field  would  be  filled. 

DIFFERENCE  BETWEEN  MAGNETO  AND  DYNAMO. 

When  the  magnetic  field  is  furnished  by  a  permanent 
magnet,  as  shown  in  the  illustrations,  the  machine  is  knowrn 
as  a  Magneto,  and  when  an  electro-magnet  is  employed,  it  is 
called  a  Dynamo.  In  the  dynamo,  part  of  the  current  gen- 
erated by  the  armature  is  used  to  energize  the  field  magnet. 
When  the  two  ends  of  the  field  winding  are  connected  re- 
spectively to  the  two  brushes,  the  current  from  the  arma- 
ture divides,  a  small  part  flowing  through  the  field  coil  and 
the  rest  out  and  away  through  the  main  circuit.  This  is 
known  as  a  Shunt  Wound  dynamo. 

If  a  dynamo  of  this  type  were  short-circuited,  a  power- 
ful rush  of  current  would  take  place,  lasting,  however,  only 
a  moment,  then  all  generation  of  current  would  cease.  This 
is  due  to  the  fact  that  the  current  would  no  longer  divide 
at  the  brushes,  but  all  of  it  would  flow  across  the  short  cir- 
cuit and  leave  nothing  to  energize  the  field  magnet,  which 

80 


Dynamic  Electricity 


would  then  rapidly  lose  its  magnetism,  when,  of  course,  no 
current  could  be  generated  by  the- armature.  When  the 
machine  is  at  rest,  there  is  practically  no  magnetism  in  the 
field ;  a  very  little  only  is  retained  by  the  soft  iron  of  the 
field  core.  When  the  dynamo  is  started,  this  "residual" 
magnetism  is  usually  strong  enough  to  produce,  in  the  arma- 
ture, a  feeble  current,  which  flows  into  the  field  winding, 
thereby  strengthening  the  magnetic  field. 

SHUNT  WOUND. 

Quite  often  a  dynamo,  particularly  if  it  has  been  idle 
for  a  long  time,  will  not,  when  started  up,  begin  to  generate 
current  or  "pick  up"  at  once.  This  may  be  due  to  a  lack 
of  residual  magnetism,  and,  if  a  battery  is  connected  for  a 
moment  to  the  field  coil,  the  machine  will  invariably  pick 
up  immediately.  The  polarity  of  the  battery  may  have  to  be 
reversed,  before  meeting  with  success.  If  a  Shunt  Wound 
Dynamo  is  connected  to  a  circuit  of  too  low  resistance,  most 
all  of  the  current  will  flow7  over  this  circuit,  and  there  will 
not  be  enough  left  to  properly  excite  the  field.  Under  these 
conditions,  the  dynamo  will  give  out  only  a  fraction  of  its 
capacity.  In  this  event,  the  resistance  of  the  main  circuit 
should  be  increased  or  a  dynamo,  wound  for  a  lower  volt- 
age, used. 

SERIES  WOUND. 

If  the  field  winding  is  of  large  size  ware,  and  connected 
in  series  with  the  armature,  the  total  current  will  flow 
through  the  field  coil  on  its  way  to  the  main  circuit.  A 
dynamo,  connected  in  this  way,  is  said  to  be  series  wound. 
The  Shunt  connection  is  generally  used,  however,  as  it  is 
less  troublesome. 

81 


Ignition 

The  variation  of  voltage  with  speed  is  greater  in  a 
dynamo  than  in  a  magneto,  because,  in  the  former  the 
strength  of  the  field  changes  with  the  speed,  and  in  the  latter 
the  magnetic  field  is  always  constant.  For  this  reason,  a 
magneto  generator  is  not  so  dependent  upon  the  circuit  with 
which  it  is  connected. 


82 


Chapter  Eleven 

Low- Tension  Dynamos— Direct  and 
Alternating   Current— Low- 
Tension  Magnetos 

Having  discussed  the  fundamental  principles  of  dyna- 
mos and  magnetos  we  will  now  see  how  they  are  made  and 
operated.  There  are  several  different  classes  of  low-tension 
machines,  viz. :  Dynamos,  generating  direct  current,  a  part 
of  which  is  used  to  energize  the  electro-magnet  fields,  and 
therefore  permanent  magnets  are  not  used ;  magnetos,  hav- 
ing permanent  magnets  for  the  field,  generating  either 
direct  or  alternating  current;  and  a  few  odd  types  of  mag- 
neto generators  which  produce  intermittent  impulses  of 
current  by  a  reciprocal  or  oscillatory  movement  of  some 
part  of  the  machine. 

THE  LOW-TENSION  DYNAMO. 

The  low-tension  ignition  dynamo  is  built  along  practi- 
cally the  same  lines  as  the  large  dynamos  used  in  power  sta- 
tions. The  electro  field  magnet,  having  its  poles  shaped  to 
fit  the  armature,  may  assume  several  different  forms.  For 
stability  and  appearance  it  is  well  to  have  it  so  shaped  as  to 
act  as  a  housing  for  enclosing  the  whole  machine.  The  pole 
pieces  are  cast  integral  therewith  as  inside  projections, 
around  which  are  placed  the  field  windings.  The  armature 
is  usually  of  the  "drum"  type  and  may  have  from  six  to 

83 


84 


Low-Tension   Dynamos — Direct   and  Alternating  Current — 
Low-Tension  Magnetos 

twelve  coils  wound  with  double  cotton  covered  wire,  care- 
fully insulated  from  the  armature  core.  The  coils  should 
be  given  a  thick  coat  of  some  oil  and  heatproof  insulating 
varnish.  If  the  winding  of  the  armature  is  not  carefully 
done,  one  or  more  of  the  coils  will,  sooner  or  later,  become 
short-circuited  or  grounded,  and  the  output  of  the  machine 
seriously  impaired.  If  the  armature  is  run  at  high  speed  as 
is  usually  the  case,  binding  wires  should  be  placed  around 
the  armature  to  prevent  the  coils  from  flying  out  of  place  by 
centrifugal  force. 

THE  COMMUTATOR. 

The  commutator  is  another  delicate  part  to  manufac- 
ture. The  copper  segments  must  be  securely  held  in  place 
and  insulated  one  from  another  and  the  ground,  by  a  special 
form  of  mica.  The  ends  of  the  coils  are  placed  in  grooves 
in  the  commutator  segments  and  soldered.  The  armature 
is  then  placed  in  a  lathe  and  the  commutator  turned  per- 
fectly smooth  and  polished.  The  brushes  are  usually  made 
of  copper  gauze,  rolled  or  folded  under  pressure  into  a 
short  rod,  one  end  of  which  is  dipped  into  melted  solder, 
to  keep  it  from  unravelling.  A  spiral  spring  is  also  attached 
to  it.  These  brushes  are  often  made  with  a  little  graphite, 
which  reduces  the  wear  on  the  commutator  and  prevents 
cutting.  Carbon  rod,  made  with  graphite,  wears  better  than 
any  other  material,  but,  owing  to  its  comparatively  high 
resistance,  it  is  not  often  used  for  low-tension  machines. 
This  objection,  however,  can  be  overcome,  to  a  large  extent, 
by  heavily  copper-plating  the  carbon.  Care  should  be  taken 
that  good  electrical  contact  is  always  maintained  between  the 
brush  and  the  brush  holder.  Missing  explosions  can  often 
be  traced  to  a  brush  that  is  not  in  good  contact  with  its 

85 


Ignition 

holder.  The  spring  should  be  just  stiff  enough  to  hold  the 
brush  firmly  against  the  commutator.  If  it  is  not  stiff 
enough,  sparking  is  likely  to  occur,  which  will  burn  and 
roughen  the  commutator,  making  good  contact  impossible. 
In  this  case  the  armature  should  be  placed  in  a  lathe  and 
the  commutator  smoothed  up  with  very  fine  sand  paper, 
and  then  rubbed  with  a  piece  of  oily  waste,  if  a  stick  of 
regular  commutator  compound  is  not  handy. 

Since  the  brushes  and  commutator  are  responsible  for 
nine-tenths  of  the  trouble  with  direct-current  dynamos  and 
magnetos,  a  frequent  inspection  of  these  parts  is  greatly 
desirable.  If  the  commutator  is  well  made,  protected  from 
dust  and  dirt,  and  large  brushes  are  used  and  inspected  once 
in  a  while,  there  is  no  excuse  for  trouble  of  any  kind. 

Where  current  for  ignition  only  is  needed,  the  dynamo 
has  been  largely  replaced  with  the  direct-current  magneto, 
but  where  it  is  also  required  to  furnish  current  for  several 
small  electric  lamps,  as  for  an  electrically  lighted  automobile 
or  small  launch,  the  dynamo  is  usually  used. 

In  order  to  get  the  best  results  from  a  spark  coil,  and 
particularly  from  low  voltage  tungsten  lamps,  it  is  neces- 
sary to  keep  the  voltage  applied  to  them  uniform  in  value. 
This  is  often  accomplished,  to  a  certain  extent,  by  building 
a  governor  into  the  machine,  which  does  not  allow  the  arma- 
ture to  rotate  above  a  certain  speed.  Most  governors,  how- 
ever, do  not  work  accurately  enough  to  keep  the  voltage 
as  uniform  as  it  should  be  for  tungsten  lamps.  To  further 
regulate  the  voltage,  the  dynamo  is  often  connected  to  a 
storage  battery  in  such  a  manner  as  to  be  constantly  charg- 
ing it  while  the  battery  is  supplying  current  for  the  ignition 
and  lamps.  A  switch  worked  by  an  electro-magnet,  or  by  a 

86 


Low-Tension  Dynamos — Direct  and    Alternating   Current — 
Low-Tension  Magnetos 


governor  on  the  dynamo,  must  be  provided  to  disconnect 
the  battery  from  the  dynamo,  when  the  latter  is  stopped 
or  not  up  to  speed,  otherwise  the  battery  would  send  a  cur- 
rent through  the  winding  of  the  dynamo  and  rapidly  dis- 
charge. If,  on  the  other  hand,  the  dynamo  is  allowed  to 
run  all  the  time,  continually  charging  the  battery,  when  the 


Zonii'ion   Systems. 


Diagram    showing    the    connections    for    a    combination    ignition 

and    lighting    system    known    as    "floating    the 

battery    on   the   line." 

lights  are  not  turned  on,  the  battery  will  become  over- 
charged, and,  if  prolonged,  it  will  be  injured.  There  are 
storage  batteries  with  liquid  electrolytes,  made  especially  for 

87 


bO  03 
g   6 


88 


Low-Tension   Dynamos — Direct   and  Alternating    Current — 
Low-Tension  Magnetos 

this  service,  that  will  stand  considerable  overcharging.  The 
water  in  the  electrolyte  will,  however,  be  "boiled"  out  and 
must  be  replaced,  from  time  to  time,  with  pure,  distilled 
water.  It  is  very,  important  to  keep  the  electrolyte  well 
above  the  plates  of  the  cells  at  all  times.  It  is  a  very  good 
thing  to  install  a  low-reading  zero-center  ammeter  in  series 
with  the  battery,  and  a  voltmeter  in  multiple  with  it,  as 
shown  by  the  diagram.  When  the  pointer  of  the  ammeter 
swings  to  the  right,  the  battery  is  being  charged,  and  to 
the  left,  discharged.  The  voltmeter  will  indicate  the  condi- 
tion of  the  battery.  If  a  regular  six-volt  battery  is  used 
and  the  voltmeter  shows  7  to  7.5  volts,  while  the  battery  is 
charging,  at  a  rate  of  2  to  4  amperes,  the  dynamo  should 
be  disconnected,  since  the  battery  is  fully  charged.  This 
system  is  known  as  " floating --the  battery  on  the  line,"  and 
will  give  excellent  results  if  a  little  care  is  used  in  han- 
dling it. 

There  are  several  special  methods  for  regulating  the 
output  of  dynamos,  such  as  having  the  governor,  instead  of 
regulating  the  speed  of  the  armature,  control  a  variable 
resistance,  in  series  with  either  the  field  winding  or  the 
main  circuit ;  or  by  having  a  compound  winding  on  the  field 
so  arranged  with  an  electro-magnetic  mechanism  that,  when 
the  voltage  exceeds  a  certairi  value,  the  field  windings  will 
oppose  each  other.  We  cannot,  for  lack  of  space,  go  into 
the  details  of  these  various  systems,  as  the  manufacturers 
furnish  descriptive  matter  and  instructions  for  their  own 
particular  systems. 

THE  DIRECT-CURRENT  MAGNETO. 

The  direct-current  magneto  is  exactly  the  same  as  the 
dynamo,  except  that  permanent  magnets  are  used  for  the 

89 


90 


Low-Tension    Dynamos — Direct  and    Alternating  Current — 
Low-Tension  Magnetos 

field.     The  armature,  commutator  and  brushes  require  the 
same  care  as  in  the  dynamo. 

Direct-current  magnetos  are  usually  made  a  little 
smaller  and  cheaper  than  dynamos,  and  are  more  popular 
where  current  is  wanted  for  ignition  only,  or  for  one  or  two 
small  tungsten  lamps.  The  magneto  has  an  advantage  over 
the  dynamo,  in  that  the  strength  of  the  field  magnet  is  the 
same  at  all  speeds.  This  allows  the  magneto  to  generate 
current  at  a  slightly  lower  speed  than  the  dynamo,  and  the 
variation  of  voltage  with  speed  is  not  as  great.  If  the 
magnets  are  carefully  made  by  up-to-date  methods,  from  the 
best  special  magnet  steel,  they  will  last  for  several  years, 
without  recharging.  It  is  very  important  in  installing  a 
magneto,  to  make  sure  that  the  voltage  it  gives  is  suited  to 
the  coil  that  is  to  be  used  with  it.  If  the  voltage  is  too  high, 
the  contact  points  on  the  coil  will  soon  burn  up,  and,  if  too 
low,  the  vibrator  will  not  work  and  the  engine  will  miss  fire. 
If  the  magneto  and  spark  coil  are  purchased  from  two  dif- 
ferent concerns,  one  or  both  of  the  manufacturers  should 
be  consulted,  as  to  whether  or  not  the  combination  will  work 
satisfactorily.  Some  magnetos  will  give  current  enough  to 
operate  the  coil  when  the  engine  is  cranked  over,  but,  in 
many  cases  it  is  best  to  provide  a  battery  for  starting. 

THE  ALTERNATING  CURRENT  MAGNETO. 
When  an  electric  current  is  constantly  changing  in 
strength  and  periodically  reversing  its  direction,  it  is  known 
as  an  alternating  current.  Alternating  current  magnetos 
cannot,  under  any  condition,  be  used  to  charge  storage  bat- 
teries. Some  alternating  current  magnetos  have  one  coil 
only  on  the  armature,  and  give  one  positive  and  one  nega- 

91 


92 


Low-Tension   Dynamos — Direct  and  Alternating    Current — 
Low-Tension  Magnetos 

tive  impulse  of  current  every  revolution.  This  type  of 
magneto  must  be  geared  to  the  engine  in  such  a  manner  that 
the  current  wave  will  be  at  its  maximum  value  at  the  instant 
ignition  is  required.  One  end  of  the  winding  is  usually 
grounded  on  the  armature  core,  and  the  other  end  is  brought 
to  an  insulated  copper  ring,  against  which  bears  a  collecting 
brush.  While  this  collecting  ring  and  brush  is  less  trouble- 
some than  a  regular  commutator,  it  should  occasionally  be 
cleaned  and  inspected. 

THE  INDUCTOR  TYPE  ALTERNATING  CURRENT  MAGNETO. 
There  are  a  few  patented  alternating  current  magnetos 
on  the  market,  which  have  no  commutator,  brushes,  collect- 
ing rings  or  moving  wires  of  any  kind.  An  alternating  cur- 
rent is  induced  in  a  stationary  winding  by  rapidly  shifting 
the  magnetic  lines  of  force  through  it.  The  only  moving 
part  of  the  machine  is  a  soft  iron  member  called  the  induc- 
tor, which  is  so  shaped  as  to  cause  the  magnetism  to  alter- 
nate through  the  coil  four  times  in  one  revolution,  thereby 
producing  four  impulses  of  current — two  positive  and  two 
negative.  Referring  to  the  drawing,  the  full  line  shows 
one  path  taken  by  the  magnetic  lines  through  'the  soft  iron 
inductor  and  stationary  winding,  and  the  dotted  line  shows 
the  other  path  in  the  reverse  direction.  Inductors  were  tried 
which  gave  six  and  even  eight  alternations  of  magnetism 
per  revolution,  but  it  was  found  that,  at  high  speed,  the 
magnetic  lines  could  not  reverse  through  the  inductor 
rapidly  enough  and  so  the  current  impulses  were  too  weak 
to  satisfactorily  operate  a  coil.  Four  impulses  of  current 
per  revolution  is  the  most  satisfactory.  Care  must  be  taken 
in  designing  an  inductor  type  magneto  to  see  that  the  pole 
pieces  and  inductor  are  so  shaped  as  to  cause  the  magnetic 

93 


Ignition 

reversals  through  the  winding  to  be  as  uniform  as  possible, 
in  order  to  insure  what  is  known  as  a  "Sine  Wave."  While 
there  are  four  impulses  of  current  per  revolution,  there  are 
also  four  times  when  the  current  is  zero.  It  is  evidently 
desirable,  then,  to  have  the  time  during  which  little  or  no 
current  is  being  produced,  as  short  as  possible.  The  two 
oscillograms  show  the  current  wave  forms  of  two  different 
inductor  type  machines.  Notice  that  one  wave  is  more 
"peaked"  than  the  other. 

If  a  machine,  giving  four  impulses  of  current  per  revo- 
lution, is  speeded  up  to  2,000  revolutions  per  minute,  there 
will  be  8,000  impulses  of  current  per  minute,  or  133  every 
second.  When  this  is  used  as  a  source  of  current  for  a 
vibrating  coil,  working  through  a  regular  timer,  it  is  evi- 
dent that  the  timer  may  happen  to  make  contact  at  the  in- 
stant when  little  or  no  current  is  being  produced.  When 
this  happens,  the  vibrator  must  wait  until  the  next  impulse 
or  wave  becomes  strong  enough  to  operate  it.  This  will  de- 
lay ignition  for  an  instant,  but,  owing  to  the  rapidity  with 
which  the  impulses  follow  one  another,  the  delay  is  too  short 
to  cause  any  appreciable  loss  of  power,  except,  perhaps, 
in  some  very  high-speed  motors. 

All  styles  of  coils  will  not,  as  a  rule,  work  satisfactorily 
on  the  inductor  type  magneto,  since  the  vibrators  and  pri- 
mary windings  will  not  respond  on  the  rapidly  alternating 
current.  A  special  coil,  or  at  least  a  special  master  vibrator, 
designed  to  work  on  alternating  current,  should  be  used  with 
inductor  type  magnetos. 

These  machines  can  be  driven  by  the  flywheel  with  a 
friction  pulley,  or  belt,  and  should  always  be  kept  up  to 
speed  as  recommended  by  the  manufacturers.  About  the 

94 


Low-Tension  Dynamos — Direct  and  Alternating  Current   - 
Low-Tension  Magnetos 

only  advantage  an  inductor  type  magneto  has  over  a  direct 
current  machine  is  the  entire  absence  of  all  brushes,  com- 
mutators, collecting  rings  and  moving  wires.  The  variation 
of  voltage  with  speed  is  also  less  than  on  direct-current  ma- 
chines, due  to  the  more  rapidly  increasing  impedance  of  the 
winding  with  speed.  On  the  other  hand,  they  have  the  dis- 
advantage of  not  being  able  to  work  successfully  on  all 
types  of  coils,  or  to  charge  storage  batteries. 


V 

1 

l^~ 

—  x 

A^. 

,  / 

\ 

/ 

% 

ft 

/ 

/ 

\ 

2 

' 

I 

\ 

\ 

l\ 

\ 

I 

V 

1 

\ 

1 

\ 

1 

\ 

\ 

1 

\ 

\ 

t 

\ 

\ 

; 

\ 

1 

\ 

/ 

/ 

\ 

/ 

\ 

/ 

\ 

/ 

\ 

\ 

/ 

*  —  ' 

Pt 

? 

s 

\ 

s 

S1 

\ 

/ 

\ 

/ 

v 

/ 

\ 

/ 

\ 

/ 

V 

/ 

s 

j 

> 

IV 

\ 

\ 

/ 

s 

/ 

\ 

k 

t 

\ 

t 

s 

1 

y 

\ 

s 

/ 

^ 

J 

sjy 

Oscillograph   records,  showing  the  current  wave   forms  of  inductor  type 

magnetos.      At    2,000    revolutions    per    minute    of    the    machine 

there  are  133  of  these  impulses  every  second. 


95 


Chapter  Twelve 

High-Tension  Magnetos— Their 
Theory  and  Construction 

Having  described  a  few  different  types  of  low-tension 
machines  it  remains  to  speak  of  the  high-tension  magneto. 
It  combines  in  one  machine — first,  a  source  of  low-tension 
current;  second,  a  commutator  or  timer,  to  allow  the  cur- 
rent to  flow  at  the  instant  ignition  is  required ;  third,  a  high- 
tension  coil  or  transformer,  to  increase  the  E.  M.  F.  of  the 
low-tension  current  to  several  thousand  volts  sufficient  for 
a  jump  spark;  and  fourth,  a  distributor,  to  connect  the  high- 
tension  current  respectively  with  the  several  cylinders  in  the 
order  of  firing. 

HIGH-TENSION  MAGNETOS. 

There  are  two  types  of  magnetos  commonly  known  as 
high-tension,  but  one  of  them  only  is,  strictly  speaking,  a 
purely  high-tension  machine,  combining  within  itself  all  four 
of  the  above  mentioned  parts.  The  other  type  contains 
within  itself  all  of  the  parts  except  the  high-tension  coil  or 
transformer,  which,  in  this  case,  is  placed  in  a  separate 
mahogany  box  or  hard  fiber  tube  and  mounted  as  near  the 
magneto  as  convenient.  A  low-tension  current  is  generated 
in  the  armature  and  sent  across  the  timer  or  breaker  points, 
where  it  is  cut  up  into  properly  timed  impulses  of  current. 
These  low-tension  impulses  are  sent  into  the  primary  wind- 
ing of  the  separate  transformer  coil,  where  they  are  changed 
to  high-tension  in  the  secondary  winding  and  sent  back 

96 


High-Tension  Magnetos — Their  Theory  and  Construction 

through  a  heavily  insulated  wire  to  the  distributor  of  the 
magneto,  where  they  are  sent  again  through  heavily  insu- 
lated wires  to  the  respective  cylinders. 

It  is  possible,  in  this  system — but  not  in  the  pure  high- 
tension  machine — to  substitute  the  current  from  a  battery 
for  that  produced  by  the  armature,  when,  of  course,  a  good 
spark  is  produced,  no  matter  how  slowly  the  machine  is 
turned  over.  This  should  be  spoken  of  as  a  Dual  system, 
and  is  highly  satisfactory  and  very  popular,  but  should  not 
be  confused  with  pure  high-tension  machines. 

THEORY  OF  THE  PURE  HIGH-TENSION  MAGNETO. 

Permanent  magnets  are  always  used  to  furnish  the  field 
magnetism  in  high-tension  magnetos.  A  common  two-pole 
or  "H"  armature  is  commonly  used,1  the  central  core  of 
which  consists  of  a  number  of  soft  iron  stampings.  As  we 
already  know,  an  armature  of  this  type  produces  two  im- 
pulses of  current  in  a  revolution — one  positive  and  one  nega- 
tive. 

In  a  previous  chapter  it  was  shown  that,  other  things 
being  equal,  the  voltage  produced  by  an  armature  increases 
directly  with  the  number  of  turns  of  wire  in  its  winding. 
Why  not,  then,  wind  an  armature  with  a  sufficient  number 
of  turns  of  fine  wire  to  produce  a  high-tension  current, 
capable  of  jumping  the  spark  gap  at  the  plug?  This  has 
been  tried,  but,  owing  to  the  small  space  available  for  wind- 
ing, it  is  impossible  to  get  on  anywhere  near  the  required 
number  of  turns ;  in  fact,  only  a  few  hundred  volts  can  be 
reached.  We  also  remember  that  a  high  voltage  is  needed 
only  to  start  an  arc,  and  only  a  few  volts  are  necessary  to 

1  There  are  a  few  special  types  of  high  tension  magnetos  employing 
either  a  stationary  winding  and  inductor,  or  a  magnetic  shield  arrangement, 
which  give  four  impulses  of  current  in  P  revolution.  In  all  other  respects, 
however,  the  principles  are  the  same.  Such  a  machine  would  be  good  for 
a  multiple-cylinder,  two-cycle  motor. 

97 


*  bfl 

ss 

be 
•rj  <u 


98 


High-Tension  Mrgnetos — Their  Theory  and  Construction 

maintain  it.  We  must,  therefore,  provide  some  other  means 
for  obtaining  a  momentary  impulse  of  high  voltage,  capable 
of  starting  the  arc,  which  can  then  be  maintained  for  a 
short  time  by  the  comparatively  low  voltage  produced  in  the 
armature.  As  we  have  already  learned,  other  things  being 
equal,  the  voltage  produced  in  an  armature  varies  directly 
with  the  speed  at  which  the  magnetic  lines  are  cut  or  made 
to  reverse  through  the  armature  winding.  As  the  armature 
revolves,  the  magnetic  reversals  do  not  take  place  instan- 
taneously, but  are  more  or  less  gradual,  thus  tending  to 
lower  the  voltage,  yet,  at  the  same  time,  prolonging  the  cur- 
rent impulses. 

Wind,  on  the  armature,  two  or  three  layers  of  rather 
coarse  wire — <say  No.  24 — and  call  it  the  Primary ;  around  it 
wind  as  many  turns  as  possible  of  carefully  insulated,  fine 
wire — say  No.  36  to  No.  40 — and  call  it  the  Secondary. 
Now,  short-circuit  the  primary  winding  and  rotate  the  arma- 
ture. The  magnetic  lines  of  force  begin  to  cut  through  the 
windings,  producing  a  current  in  the  primary  which  grad- 
ually increases  until  a  position  is  reached  where  the  maxi- 
mum number  of  lines  of  force  is  being  cut.  This  induced 
current  in  the  primary  tends  to  strengthen  the  magnetism 
in  the  armature  core.  When  the  current  in  the  short-cir- 
cuited primary  is  at  its  maximum,  suddenly  interrupt  it  by 
opening  the  circuit  and  an  almost  instantaneous  collapse 
of  part  of  the  magnetic  lines  in  the  armature  will  follow. 
This  very  rapid  change  of  magnetism  through  the  secondary 
winding  will  induce  in  it  a  momentary  impulse  of  several 
thousand  volts,  sufficient  to  start  an  arc  between  the  points 
of  the  spark  plug.  The  arc  is  then  maintained  for  a  short 
time  by  a  current  of  lower  voltage,  produced  in  the  second- 
ary winding  by  the  rotation  of  the  armature.  A  condenser 
of  small  capacity  is  connected  across  the  breaker  points  to 

99 


•d  p  M 

Sal 

cog's 
.2.2s  ? 


*.*5       w 

•£  cj^w  <u  * 


MCJ 
TJ 


ro  <u       I 

»«£l 


|9 


100 


High-Tension  Magnetos — Their  Theory  and  Construction 

prevent  the  platinum  contacts  from  burning  and  to  assist  in 
the  rapid  collapse  of  the  magnetic  lines. 

Fig.  1  shows  three  different  positions  of  an  "H"  arma- 
ture during  rotation,  and  clearly  illustrates  how  the  mag- 
netic lines  are  made  to  reverse  their  direction  through  the 
armature.  The  curve  at  the  bottom  of  the  figure  is  an  oscil- 
lograph record  of  the  current  wave,  showing  the  two  im- 
pulses of  current  during  one  revolution — one  positive  and 
the  other  negative.  The  positions  on  the  curve  marked  A', 
B'  and  C'  correspond  to  the  three  positions  of  the  armature 
shown  at  A,  B  and  C.  A  careful  study  of  the  relative  posi- 
tions will  be  of  interest,  as  we  can  briefly  mention  only  one 
or  two  of  the  most  important  points. 

Suppose  the  cam  to  be  set  so  as  to  open  the  primary 
circuit  when  the  armature  has  reached  the  position  indicated 
at  "B"  (Fig.  1).  The  wave  is  at  its  maximum  height,  so 
that  the  induced  current  in  the  Primary  winding  will  be 
strongest.  Also  notice  that,  as  the  armature  continues  to 
rotate  from  position  "B"  to  "C,"  the  curve  does  not  rapidly 
descend.  The  armature,  therefore,  cuts  the  lines  of  force  at 
almost  a  uniform  rate  during  that  period,  and,  consequently, 
the  current  produced  thereby  in  the  secondary  winding,  will 
maintain  a  strong  arc  for  a  short  time.  Again,  suppose 
the  cam  to  be  set  so  as  to  open  the  primary  circuit  when  the 
armature  has  reached  position  "C" ;  the  curve  has  begun  to 
descend,  and,  consequently  the  arc  will  not  jump  as  far  or 
be  as  strong  as  in  the  first  case.  Position  "B"  corresponds 
to  extreme  advance,  and  "C"  extreme  retard,  of  a  high- 
tension  magneto  having  a  spark  advance  range  of  40  de- 
grees. This  explains  why  the  spark  is  stronger  when  the 
magneto  is  advanced  than  when  retarded,  particularly  at 
low  engine  speeds. 

101 


Ignition 

If  the  cam  should  be  a  trifle  too  far  advanced  so  as  to 
open  the  primary  circuit  before  the  armature  reaches  the 
position  shown  at  "B,"  say  at  "d"  (indicated  on  the  curve), 
it  is  evident  that  the  spark  will  be  very  weak  and  will  not 


V} 

fc 
x 

QJ 
^ 

E 

t 


te^ 


A/o.3/. 


Complete     Revolution  of  the 


A    series    of    oscillograph    records    of    the    current    forming 

the   arc  between  the   points  of  a  spark   plug.     The  first 

two   are   taken  from   the   same   magneto  —  No.    28   at 

extreme  retard  and  No.  29   at  extreme  advance. 

Note    that    the    arc    does    not    immediately 

begin     to     die     out     on     the     advance 

position    as    it   does    on    the    retard 

102 


High  Tension  Magnetos — Their  Theory  and  Construction 

always  jump  between  the  points  of  the  plug,  causing  the 
engine  to  miss  fire.  If  the  cam  or  facing  against  which  it 
rubs,  or  the  platinum  points  should  be  badly  worn,  or  the 
platinum  tipped  contact  screw  backed  out  farther  than  it 
should  be,  the  effect  is  the  same  as  if  the  cam  were  advanced 
too  far,  and  a  short,  weak  spark  will  be  the  result.  To 
avoid  this  trouble  and  to  allow  for  a  slight  variation  in 
manufacture,  it  is  best  to  set  the  cam  so  as  to  open  the  cir- 
cuit at  a  point  well  up  on  the  curve,  in  order  that  a  slight 
advance,  due  to  wear  or  improper  adjustment  of  the  plati- 
num points,  will  not  weaken  the  spark. 

Fig.  2  is  a  series  of  oscillograph  records  of  the  current 
forming  the  arc  between  the  points  of  a  spark  plug.  The 
first  two  are  taken  from  the  same  magneto — 'No.  28  at  ex- 
treme retard  and  No.  29  at  extreme  advance.  Note  that 
the  arc  does  not  immediately  begin  to  die  out  on  the  advance 
position,  as  it  does  on  the  retard.  No.  30  is  from  a  different 
make  of  pure  high-tension  magneto  and  No.  31  is  from  a 
special  form  of  Dual  magneto,  employing  a  separate  high- 
tension  winding  in  the  form  of  a  transformer,  so  designed 
with  sufficient  magnetic  lag,  etc.,  as  to  prolong  the  arc  prac- 
tically the  same  as  a  pure  high-tension  machine.  There  is 
no  object  in  maintaining  the  arc  too  long;  in  fact  it  simply 
tends  to  burn  up  the  points  of  the  spark  plug.  The  charge 
is,  most  likely,  thoroughly  ignited  before  the  position  marked 
"X"  on  curve  No.  28,  is  reached. 


103 


Chapter  Thirteen 

The  Installation  and  Care  of 
High-Tension  Magnetos 

All  high-tension  magnetos  must  be  positively  driven. 
They  cannot,  under  any  condition,  be  driven  by  belt  or  fric- 
tion. Since  the  spark  occurs  only  when  the  armature  is  in  a 
certain  position,  the  magneto  must  be  so  timed  that  the  spark 
will  occur  at  the  instant  ignition  is  required.  The  magneto 
is  usually  connected  with  some  form  of  universal  joint, 
directly  to  one  end  of  the  cam  or  pump  shaft,  or  a  special 
short  shaft  extending  from  one  of  the  cam  shaft  gears  that 
runs  at  the  proper  speed.  The  following  table  shows  the 
different  speeds  at  which  magnetos  should  be  driven  relative 
to  the  speed  of  the  motor : 

Number   of 

cylinders.  Cycle.  Speed.  Form    of   cam. 

4  4  Crank    shaft  Double 

2  4  Crank  shaft  Single 

3  4  iy2    x   crank  shaft  Single 
6  4  iy2    x   crank  shaft                          Double 

4  2  2   x   crank   shaft  Double 

2  2  2   x   crank   shaft  Single 

3  2  iy2    x  crank   shaft  Double 
6                               2-                              3   x   crank    shaft  Double 

Fig.  6  shows  several  forms  of  couplings.  No.  1  is  the 
popular  Oldham  universal  coupling ;  No.  2  is  a  fairly  satis- 
factory device,  consisting  of  two>  pins  in  one  end  of  the 
coupling,  working  in  two  corresponding  slots  in  the  other 
end.  No.  3  shows  a  device  for  slightly  changing  the  timing 
after  both  ends  of  the  coupling  are  secured  to  the  shafts. 
When  the  two  hexagon  bolts  are  loosened,  the  magneto  end 

104 


-EP 


Fig.  6  shows  several  forms  of  couplings.  No.  1  is  the  popu- 
lar Oldham  universal  coupling;  No.  2  is  a  fairly  satisfac- 
tory device,  consisting  of  two  pins  in  one  end  of  the 
coupling,  working  in  two  corresponding  slots  in  the  other 
end.  No.  3  shows  a  device  for  slightly  changing  the 
timing  after  both  ends  of  the  coupling  are  secured  to  the 
shafts.  No.  4  consists  of  two  similar  "T"  shaped  members, 
loosely  joined  together,  with  a  star-shaped  steel  stamping, 
having  its  edges  folded  over.  No.  5  shows  a  very  poor 
coupling  which  does  not  permit  of  any  misalignment  of 
magneto  and  driving  shaft. 

105 


Ignition 

of  the  coupling  can  be  turned  as  far  as  the  slots,  through 
which  the  bolts  extend,  will  permit.  No.  4  consists  of  two 
similar  "T"-shaped  members,  loosely  joined  together,  with 
a  star-shaped  steel  stamping,  having  its  edges  folded  over. 
No.  5  shows  a  very  poor  coupling  which  does  not  permit 
of  any  misalignment  of  magneto  and  driving  shaft.  It  is 
not  economy  to  use  a  poor  coupling,  as  it  will  strain  and 
sometimes  bend  the  armature  shaft  and  cause  an  undue 
wear  of  the  bearings. 

A  rigid  shelf,  made  of  some  non-magnetic  material, 
such  as  brass  or  aluminum,  should  be  provided,  upon  which 
to  mount  the  magneto.  If  an  iron  shelf  is  used,  a  part  of 
the  magnetic  lines  will  pass  through  it,  which  tends  to 
weaken  the  spark.  It  is  best  to  locate  the  magneto  on  the 
shelf  with  dowel  pins  and  hold  it  in  place  with  a  strap  of 
sheet  brass  passing  over  the  top  of  the  magnets.  This 
makes  it  easy  to  remove  the  magneto  for  cleaning  and  in- 
specting. 

TIMING  THE  MAGNETO. 

The  following  are  the  general  rules  for  timing  a  high- 
tension  or  dual  magneto. 

Turn  the  engine  over  until  cylinder  No.  1  is  on  the  upper 
dead  center,  just  before  the  firing  stroke.  Secure  one  end 
of  the  coupling  to  the  driving  shaft  or  magneto,  whichever 
is  the  most  convenient,  and  place  the  magneto  and  other 
parts  of  the  coupling  in  position.  Turn  the  spark  advance 
lever  to  the  position  of  extreme  retard,  which  will  be  in  the 
same  direction  as  the  armature  runs.  Remove  the  cover  of 
the  interrupter  or  breaker  box,  so  that  the  contact  points 
can  be  seen,  and  slowly  turn  the  armature  in  the  direction 
it  is  to  run  until  the  contact  points  just  begin  to  separate. 

106 


The  Installation  and  Care  of  High-Tension  Magnetos 

This  point  should  be  carefully  determined.  Now  secure 
both  ends  of  the  coupling  to  the  shafts  with  taper  pins.  Re- 
move the  front  plate  or  cover  of  the  distributor  and  see  with 
what  segment  the  distributor  hand  is  in  contact.  Connect 
this  segment  with  high-tension  wire  to  the  spark  plug  of 
cylinder  No.  1,  then  connect  the  remaining  terminals  with 
the  rest  of  the  cylinders  in  the  proper  order  of  firing,  bear- 
ing in  mind  that  the  distributor  hand,  in  most  cases,  revolves 
in  the  opposite  direction  to  that  of  the  armature. 

There  is  usually  a  binding  post  on  pure  high-tension 
machines,  which,  when  connected  through  a  switch  to 
ground  on  the  engine  frame,  will  short-circuit  the  primary 
winding,  thereby  shutting  off  the  spark.  Dual  magneto  con- 
nections are  more  complicated  and  the  wiring  diagrams 
furnished  by  the  makers  should  be  carefully  followed.  Care 
must  be  exercised  in  connecting  dual  magnetos,  not  to  get 
the  battery  connected  directly  across  the  armature  winding, 
even  for  a  second,  as  'this  would  make  an  electro-magnet 
out  of  the  armature  which,  likely,  would  oppose  the  field 
magnets  and  weaken  them.  It  is  convenient  sometimes  with 
dual  magnetos  to  connect  an  electric  bell  and  dry  battery  in 
series  with  the  contact  points,  to  determine  when  the  separa- 
tion occurs.  Unfortunately,  this  cannot  be  done  with  pure- 
high-tension  machines. 

CARE  OF  HIGH-TENSION  MAGNETOS. 

A  few  hints  regarding  the  care  of  high-tension  mag- 
netos may  be  helpful.  It  is  often  a  very  good  thing  to  cover 
the  machine  with  a  rubber  or  leather  hood,  made  especially 
for  the  purpose,  since  dust,  dirt,  grease  and  particularly 
water,  are  all  enemies  of  the  magneto.  The  glass  or 
porcelain  knob,  which  covers  the  safety  spark  gap  (if  there 
is  one),  should  be  kept  clean  and  free  from  grease  and  dirt. 

107 


Ignition 

The  distributor  should  be  kept  clean  and  dry  and  the  path, 
over  which  the  carbon  distributing  brush  slides,  ought  to  be 
wiped  off  occasionally  with  a  clean  cloth,  moistened  with 
gasoline,  for  a  slight  carbon  deposit  will,  in  time,  form  be- 
tween the  segments  and  cause  misfiring.  The  spiral  spring 
behind  the  carbon  distributing  brush  must  not  be  too  stiff; 
it  should  be  just  stiff  enough  to  hold  the  brush  in  very 
light  contact  with  the  surface  over  which  it  slides. 

Fig.  3  is  a  diagrammatic  view  of  a  pure  high-tension 
magneto  and  shows  the  connections  and  relations  of  the  sev- 
eral parts.  At  the  left  is  a  sectional  view  of  the  heavily 
insulated  collecting  ring  for  leading  the  high-tension  current 
from  the  secondary  winding  on  the  armature,  to  the  distrib- 
uting hand,  from  which  it  is  sent  to  the  different  cylinders. 
When  tracing  out  the  connections,  note  that  one  end  each 
of  the  primary  and  secondary  windings  is  grounded  to  the 
armature  core.  A  safety  spark  gap  is  provided,  over  which 
the  spark  can  find  an  easy  path,  should  a  wire  come  off  of 
a  spark  plug,  thereby  preventing  unnecessary  and  dangerous 
strain  on  the  insulation  of  the  secondary  winding. 

Fig.  4  is  a  sectional  drawing  of  a  special  form  of  dual 
magneto,  which  has  the  high-tension  winding  made  in  the 
form  of  a  transformer  and  placed  under  the  arch  of  the 
magnets.  In  this  machine  as  in  all  dual  magnetos,  the  arma- 
ture has  just  one  primary  winding  of  coarse  wire. 

A  high-tension  magneto  is  not  an  easy  piece  of  appa- 
ratus to  manufacture.  The  greatest  care,  both  mechan- 
ically and  electrically,  must  be  exercised  throughout  the 
entire  construction. 

THE  MAGNETIC  CIRCUIT. 

The  magnets  should  be  carefully  made  of  the  best  mag- 
net steel  and  strongly  magnetized  and  seasoned  before  plac- 

108 


The  Installation  and  Care  of  High-Tension  Magnetos 


ing  on  the  machine.  In  order  to  make  the  magnetic  circuit 
as  good  as  possible,  the  inside  surfaces  of  the  magnets 
should  be  ground  bright  and  smooth  after  hardening,  but 
before  magnetizing,  and  the  pole  pieces  smoothed  and  all 


To      Spark   Pluqs. 


Secondary 
Collecting 
Brush,  t- 


'Distributing 

hand. 

Secondary 
D  i  stri  butinrj. 
Brush. 

ecortdary 
Windinq. 

Primary 
W'mdinq 

'Thick  J.rtsu\atioti. 


Soft    Iron 
Qrmal'ure  Core. 


Cam' 


Screw. 


Fig.     3,     a     diagrammatic     view     of     a     pure    high-tension     magneto,     which 
clearly    shows    the    connections    and    relations    of    the    several    parts. 
At    the    left    is    a    sectional    view    of    the    heavily    insulated 
collecting    ring    for    leading    the    high-tension    cur- 
rent   from    the    secondary    winding    on    the 
armature,     to     the     distributing     hand, 
from     which     it     is     sent     to     the 
different    cylinders. 

109 


Ignition 

scale  removed  so  as  to  make  a  perfect  fit  with  the  magnets. 
The  armature  should  be  made  with  only  a  few  thousandths 
of  an  inch  clearance,  but  must  not  be  close  enough  to  the 
pole  pieces  to  drag  after  the  bearings  have  become  slightly 
worn.  With  good  ball  bearings  and  workmanship,  a  clear- 
ance of  about  six  thousandths  of  an  inch  on  a  side  is  all 
that  is  necessary. 

WINDING  THE  ARMATURE. 

The  winding  of  the  armature  is  the  most  delicate  part 
of  the  work,  requiring  a  great  deal  of  patience  and  skill. 
Many  layers  of  very  fine  insulated  wire  are  used  on  the 
secondary,  each  layer  being  separated  from  its  neighbor  by 
a  turn  of  very  thin  oiled  silk  gauze.  The  whole  winding 
must  be  saturated  with  a  good,  flexible,  heat-resisting,  moist- 
ure-proof insulating  varnish,  and  covered  over  with  a  thick 
insulation  of  oiled  silk. 

COLLECTING  RING  AND  BRUSH. 

The  problem  of  leading  the  high-tension  current  away 
from  the  armature  is  not  an  easy  one,  and  the  collecting  ring 
should  be  made  of  the  best  grade  of  hard  rubber,  ample  in 
size,  with  as  great  a  sparking  distance  to  ground  as  possible. 
It  must  also  be  protected  from  oil  and  dirt.  The  carbon 
brush  should  bear  lightly  on  the  brass  ring  and  be  carefully 
insulated  from  ground. 

THE  CONDENSER. 

The  condenser,  in  many  machines,  is  made  of  alternate 
washers  of  tin  foil  and  mica,  assembled  over  the  shaft  at 
one  end  of  the  armature,  and  should  be  protected  by  a  thin, 
brass  case.  In  other  machines  it  consists  of  alternate  sheets 
of  tin  foil  and  mica,  assembled  in  a  brass  or  aluminum  case, 
placed  under  the  arch  of  the  magnets. 

110 


The  Installation  and  Care  of  High-Tension  Magnetos 

THE  INTERRUPTER. 

The  interrupter  or  breaker  assumes  many  different 
forms,  but  the  principle  in  all  cases  is  the  same.  In  many 
pure  high-tension  machines,  it  is  -made  to  rotate  with  the 
armature  and  two  stationary  fiber  pieces  act  as  cams  to 
effect  a  separation  of  the  platinum  points.  The  main  thing 
about  an  interrupter  is  to  have  it  light  and  responsive,  so 
that,  at  high  speeds,  it  will  not  miss  contact  as  some  earlier 
forms  are  apt  to  do.  There  are,  unfortunately,  a  few  of 
these  still  on  the  market.  Dual  magnetos  have  the  inter- 
rupter mounted  stationary  and  effect  a  separation  of  the 
contacts  by  a  cam  attached  to  the  armature  shaft,  bearing 
against  a  steel  roller,  or  steel  or  fiber  facing  attached  to  the 
interrupter  arm. 

SAFETY  SPARK  GAP. 

The  wire  or  spring  clip,  which  connects  the  collecting 
brush  with  the  distributing  hand,  must  be  widely  separated 
and  insulated  from  the  ground  or  metal  parts  of  the  mag- 
neto. The  safety  spark  gap  is  often  placed  under  this  strip 
and  protected  from  dirt  and  water  by  a  glass  or  porcelain 
insulator.  The  gap  is  usually  about  T%  inch  long,  and,  if  it 
is  wet  or  dirty,  or  too  short,  the  spark  will  jump  or  creep 
across  it  rather  than  take  the  gap  between  the  points  of  the 
spark  plug,  particularly  if  they  happen  to  be  rather  widely 
separated,  and  irregular  missing  of  explosion  will  result.  In 
some  pure  high-tension  machines,  the  safety  gap  is  located 
on  one  end  of  the  armature  near  the  winding. 
HIGH-TENSION  DISTRIBUTOR. 

There  are  two  general  forms  of  distributor,  the  passing 
contact,  where  the  spark  is  made  to  jump  a  small  air  gap 
between  the  distributing  hand  and  brass  segments ;  and  the 

111 


112 


The  Installation  and  Care  of  High-Tension  Magnetos 

rubbing  contact,  where  a  carbon  brush  is  made  to  slide 
from  one  brass  segment  to  the  next.  The  passing  contact 
is  cheaper  to  manufacture  than  the  other,  but  is  not  consid- 
ered as  good  because  some,  energy  is  lost  in  forcing  the 
spark  across  the  air  gap.  If  this  gap  could  be  kept  less 
than  1-64  inch  at  all  times,  this  objection  would  be  over- 
come, but  it  is  impracticable,  for  mechanical  reasons,  to  do 
so.  It  is  well  to  mold  the  brass  segments  into  a  block  of 
special  hard  rubber  and  then  smooth  up  in  a  lathe  the  sur- 
face against  which  the  carbon  brush  rubs.  The  distributing 
hand  must  be  driven  by  gears  from  the  armature  shaft  at 
such  a  speed  that  it  will  be  in  contact  with  a  brass  segment 
at  the  instant  the  interrupter  points  are  separated. 

Fig.  5  is  a  photograph  of  a  pure  high-tension  magneto 
partly  disassembled.  A  is  the  high-tension  winding  on  the 
armature ;  B  the  collecting  ring ;  C  the  carbon  collecting 
brush  and  hard  rubber  holder ;  D  the  hard  rubber  protector 
and  brush  that  leads  the  high-tension  current  into  the  dis- 
tributing hand ;  E  the  distributing  hand  and  carbon  brush ; 
F  the  special  form  of  interrupter  that  rotates  with  the  arma- 
ture; G  the  spark  advance  lever,  showing  the  stationary 
fiber  cams ;  H  the  porcelain  safety  spark  gap  protector,  and 
7  the  small  carbon  brush  which  leads  the  primary  current  to 
the  switch  for  grounding  to  stop  the  magneto.  The  con- 
denser is  mounted  on  the  left  hand  end  of  the  armature  and 
does  not  show. 

The  contact  points  should  not  separate  more  than  the 
thickness  of  an  ordinary,  rather  thin  business  card,  and 
should  they  become  badly  pitted,  they  must  be  made  smooth 
with  a  very  fine  file  or  replaced  with  new  ones. 

113 


53  rt 

6  bo 


e-«S 

ill 


114 


The  Installation  and  Care  of  High-Tension  Magnetos 

Most  magnetos  are  provided  with  three  or  more  oil 
holes,  which  should  receive  a  few  drops  of  high  grade  thin 
oil  several  times  a  season,  according  to  how  much  the  ma- 
chine is  used.  It  is  not  well  nor  necessary  to  flood  the  ma- 
chine with  oil,  neither  should  it  be  run  dry.  The  ball  bear- 
ings are  packed  with  hard  grease  before  the  machines  leave 
the  factory,  and  so  very  little  oiling  is  necessary  for  the 
first  few  months'  use. 

There  is  nothing  difficult  about  caring  for  a  magneto. 
If  these  few  simple  things  are  systematically  looked  after, 
trouble  with  the  magneto  is  not  likely  to  develop. 


115 


Chapter  Fourteen 

Low- Tension  Positively  Driven 

Make-and-Break  Magnetos 

for  Stationary  Engines 

The  newest  type  of  ignition  receiving  the  attention 
of  progressive  manufacturers  of  stationary  farm  en- 
gines, is  a  gear-driven  magneto,  the  armature  of  which 
is  designed  to  act  as  a  make  and  break  coil  as  well  as 
to  perform  its  regular  function  of  generating  the  cur- 
rent. With  this  type  of  magneto  the  make-and-break 
coil  and  batteries  are  entirely  eliminated  and  the  mag- 
neto made  a  permanent  part  of  the  engine,  thereby 
making  the  system  extremely  simple. 
OPERATION  OF  SYSTEM. 

A  two-pole  or  "H"  armature  is  made  to  revolve 
between  the  poles  of  a  permanent  magnet.  The  arma- 
ture has  a  single  winding,  one  end  of  which  is  grounded 
to  the  armature  core.  The  other  end  is  brought  out 
to  a  collecting  ring  against  which  bears  a  collecting 
brush.  This  brush  is  connected  to  the  insulated  point 
of  the  igniter  on  the  engine.  The  armature  is  posi- 
tively driven  from  the  crank  or  cam  shaft  so  that  the 
current  impulses  will  be  at  their  maximum  strength 
the  instant  ignition  is  required.  When  the  armature 
starts  to  revolve  a  current  is  produced  in  its  winding, 

116 


Low-Tension  Positively  Driven  Make-and-Break  Magnetos 

for  Stationary  Engines 

which  passes  out  through  the  collecting  ring  and  brush 
to  the  igniter  points,  which  are  now  in  contact,  then 
to  the  ground  and  back  through  the  frame  of  the  en- 
gine and  magneto  to  the  grounded  end  of  the  winding. 
The  current  begins  to  build  up  and  strengthens  the 
magnetism  in  the  armature.  When  the  current  has 
reached  its  maximum  the  igniter  points  separate, 
after  which  the  armature  acts  as  a  make-and-break 
coil  and  delivers  the  energy  stored  in  it  to  the  igniter 
points  in  the  form  of  an  arc  similar  to  that  produced 
by  a  battery  and  make-and-break  coil.  This  process 
is  repeated  for  every  ignition,  and  the  armature  is  con- 
stantly changing  from  acting  as  a  generator  of  current 
to  a  make-and-break  coil.  This  system  as  a  whole  is 
very  simple,  but  great  care  must  be  taken  in  properly 
designing  all  of  the  parts. 

CONSTRUCTION  OF  MAGNETO. — FIELD  MAGNETS. 

The  best  grade  of  permanent  steel  magnets  should 
be  used  for  furnishing  the  field  magnetism.  The  pole 
pieces  must  be  fitted  perfectly  to  the  magnets  and 
should  be  made  of  the  best  grade  of  soft  "magnetic" 
cast  iron. 

ARMATURE. 

The  armature  core  should  be  cast  from  a  special 
grade  of  soft  magnetic  iron  having  a  high  magnetic 
permeability  at  low  densities.  In  order  to  reduce 
the  reluctance  of  the  magnetic  circuit  as  much  as  pos- 
sible, the  cross  sectional  area  of  the  core  must  be  made 
large  enough  to  easily  carry  all  the  magnetic  lines 

117 


bo 

<u  C 


118 


Low-Tension  Positively  Driven  Make-and-Break  Magnetos 
for  Stationary  Engines 

from  one  pole  piece  to  the  other,  and  the  clearance 
between  the  pole  pieces  and  armature  should  not 
exceed  eight  thousandths  of  an  inch.  On  the  other 
hand,  the  armature  must  not  run  close  enough  to  the 
pole  pieces  to  rub  should  the  bearings  become  slightly 
worn. 

The  armature  has  a  single  winding  of  silk  insu- 
lated wire,  varying  with  different  makes  of  machines 
from  No.  22  to  No.  32  B.  &  S.  gage.  One  end  of  the 
winding  is  grounded  by  soldering  to  the  armature  core, 
and  the  other  end  is  connected  to  the  insulated  collect- 
ing ring. 

GROUNDING  BRUSH. 

The  current  is  led  away  from  the  machine  by  the 
collecting  ring  and  brush,  and  the  return  circuit  passes 
through  the  engine  frame  into  the  frame  of  the  mag- 
neto and  back  to  the  grounded  end  of  the  armature 
winding.  The  bearings,  however,  must  not  be  depend- 
ed upon  for  carrying  the  current  to  the  armature 
winding.  The  film  of  oil  which  surrounds  the  shaft 
acts  as  a  high  resistance  and  prevents  a  steady  flow 
of  current.  If  the  current  is  forced  across  this  film  of 
oil  a  sort  of  electrolysis  of  the  steel  shaft  wrill  take 
place,  which  will  not  only  destroy  the  oil  but  will 
roughen  the  shaft  and  bearing. 

There  are  various  forms  of  grounding  brushes 
such  as  plain  copper  gauze  brushes,  gauze  brushes 
saturated  with  graphite,  and  carbon  brushes.  These 
brushes  are  usually  round  and  are  made  to  bear  against 
the  bronze  end  of  the  armature  cap.  The  graphite 
saturated  copper  gauze  brush  is  very  satisfactory. 

119 


120 


Low-Tension  Positively  Driven  Make-and-Break  Magnetos 
for  Stationary  Engines 

COLLECTING  RING  AND  BRUSH. 

It  is  not  easy  to  design  a  collecting  ring  and 
brush  that  will  operate  continuously  without  any 
attention.  There  are  several  different  methods  which 
have  been  used  with  more  or  less  satisfaction. 

In  some  machines  one  end  of  the  armature  shaft 
has  a  hole  bored  lengthwise  through  it,  in  which 
is  placed  an  insulated  copper  or  steel  rod,  the  outer 
end  of  which  terminates  in  a  copper  button  or  better, 
a  steel  disc.  If  steel  is  used,  it  should  be  highly 
polished  and  glass  hard.  A  gauze  or  carbon  brush 
is  arranged  to  bear  against  the  center  of  the  steel 
button.  It  is  better,  however,  to  place  two  smaller 
brushes  near  the  outside  edge  of  the  steel  disc,  so 
that  the  wear  on  the  brushes  will  be  more  uniform 
and  the  surface  will  be  kept  cleaner  than  if  one  larger 
brush  were  used  against  the  center  of  the  disc.  In 
some  constructions  the  steel  disc  is  replaced  with  a 
short  length  of  steel  shaft  and  one  or  two  brushes 
made  to  bear  on  the  side  of  this  shaft.  This  is  not 
as  satisfactory,  however. 

Good  electrical  contact  between  the  brush  and  the 
surface  over  which  it  slides  is  necessary,  because  if 
the  brush  starts  sparking  it  will  rapidly  wear,  and  the 
sparking  action  will  roughen  the  surface  and  cause 
imperfect  contact.  A  very  satisfactory  arrangement 
is  a  special  carbon  brush  about  5/16  of  an  inch  in 
diameter  bearing  lightly  against  the  surface  of  a  flat 
ring  made  of  hard  commutator  copper.  Brass  or 
steel  is  in  no  way  as  good  as  this  particular  form  of 

121 


Ignition 

copper.  The  carbon  brush  can  be  greatly  improved 
by  having  it  made  with  a  little  graphite  which  acts 
as  a  lubricant,  thereby  reducing  friction  and  wear. 
It  should  also  be  heavily  copper  plated  to  reduce  the 
electrical  resistance.  The  copper  ring  must  be  care- 
fully insulated  from  ground.  Washers  of  hard  white 
fiber,  1/16  of  an  inch  thick  are  good  for  this  purpose. 
Figure  1  is  a  drawing  showing  the  detailed  construc- 
tion of  the  collecting  ring  and  brush  holder.  The 
brush  holder  must  also  be  well  insulated  and  firmly 
fastened  so  as  not  to  work  loose.  It  is  very  important 
that  the  brush  make  a  good  electrical  contact  with 
its  holder,  and  at  the  same  time  be  free  to  slide  in  and 
out  so  that  a  light  spiral  spring  will  be  sufficient  to 
hold  it  firmly  against  the  copper  ring. 

BEARINGS. 

Needless  to  say  the  bearings  should  be  provided 
with  an  oil  chamber  of  ample  capacity  so  that  fre- 
quent attention  will  not  be  necessary.  In  order  to 
protect  the  armature  from  dust  and  moisture  a  tight 
fitting  cover  over  the  housing  should  be  provided. 
This  also  will  prevent  iron  filings  from  being  drawn 
in  between  the  pole  pieces  by  the  magnetic  attraction. 
A  felt  washer  fitted  snugly  over  the  shaft  between 
the  bearing  and  the  collecting  ring  will  help  materially 
in  keeping  oil  away  from  the  armature  and  brush. 
CURRENT  WAVES. 

The  armature  does  not  give  a  steady  flow  of  cur- 
rent like  a  battery  or  dynamo,  but  gives  two  sep- 
arate impulses  of  current  every  revolution — one  posi- 
tive and  one  negative.  These  impulses  or  current 

122 


Low-Tension  Positively  Driven  Make-and-Break  Magnetos 
for  Stationary  Engines 

waves,  as  they  are  called,  build  up  gradually  and  die 
down  still  more  gradually.  From  this  it  follows  that 
the  armature  must  be  positively  driven  by  the  engine 
so  that  a  current  wave  will  be  at  its  maximum  strength 
at  the  instant  the  igniter  points  separate.  The  cur- 
rent wave  must  not  be  "peaked"  but  should  be  as 
"flat"  as  possible  so  that  any  lost  motion  in  the  driv- 
ing gears,  or  wear  of  igniter  points,  will  not  cause 
the  latter  to  separate  when  the  wave  is  weak  or  at 
zero  value. 

In  order  to  take  care  of  the  advance  and  retard 
of  spark  the  wave  must  be  flat  enough  to  permit  the 
necessary  variation,  or  the  whole  magneto  must  be 
mounted  so  that  it  can  be  revolved  through  as  many 
degrees  as  there  is  spark  advance.  With  this  latter 
system  when  the  engine  is  being  started,  the  mag- 
neto is  tilted  in  the  same  direction  the  armature  runs 
and  the  spark  lever  retarded.  This  shifts  the  cur- 
rent wave  so  that  it  will  be  at  its  maximum  when 
the  igniter  points  separate.  The  form  of  the  current 
wave  depends  principally  upon  the  shape  of  the  arma- 
ture core  and  pole  pieces,  the  magnetic  permeability 
of  the  iron  from  which  they  are  cast,  and  the  winding 
on  the  armature. 

Following  is  an  oscillograph  record  of  the  cur- 
rent and  open  circuit  E.  M.  F.  waves  of  a  well-designed 
magneto.  The  current  wave,  of  course,  does  not  follow 
the  shape  of  the  E.  M.  F.  wave,  but  is  materially  flat- 
tened, due  to  the  reactance  of  the  armature  winding. 
If  the  resistance  of  the  armature  winding  is  too  high 

123 


124 


Low-Tension  Positively  Driven  Make-and-Break  Magnetos 
for  Stationary  Engines 

the  current  will  be  choked  and  will  not  respond  as 
rapidly  as  it  should.  On  the  other  hand,  if  it  is  too 
low  the  current  will  not  persist  long  enough,  thereby 
shortening  the  duration  of  the  arc.  The  amperage 
will  also  be  increased,  which  will  more  rapidly  destroy 
the  igniter  points.  The  current  wave  on  this  magneto 
is  strong  enough  to  produce  a  good  spark  during 
about  40  degrees  of  revolution.  This  is  ample  to  per- 
mit a  considerable  variation  of  adjustment  between 
the  armature  and  igniter  points. 

TIMING  THE  MAGNETO. 

Any  good  coupling  such  as  is  used  for  high 
tension  magnetos,  or  a  set  of  gears,  can  be  used 
to  drive  the  magneto.  There  is  usually  a  mark  placed 
on  the  magneto  armature,  by  the  manufacturer,  to 
show  the  position  it  is  in  when  the  current  wave  is 
at  its  maximum  strength.  This  occurs  at  the  instant 
the  edge  of  the  armature  core  has  pulled  away  from 
the  edge  of  the  pole  piece  about  1-16  of  an  inch. 

The  timing  is  very  simple.  Turn  the  engine  over 
slowly  until  the  igniter  points  just  snap  apart;  then 
turn  the  magneto  in  the  direction  it  is  to  run  until 
the  armature  has  pulled  away  from  the  pole  piece  1-16 
of  an  inch,  or  as  shown  by  the  marks  on  the  armature. 
Now  secure  the  magneto  in  place  and  connect  a  wire 
from  the  collecting  brush  to  the  igniter.  The  mag- 
neto can  be  run  in  either  direction. 

If  the  magneto  is  not  mounted  on  a  metal  base 
which  is  in  good  electrical  contact  with  the  engine 
frame,  it  will  be  necessary  to  ground  it  by  connecting 
a  wire  from  the  body  of  the  magneto  to  the  frame 

125 


A    typical    installation — the    magneto    is    gear    driven    at    engine 
speed    from    the    cam    shaft. 


126 


Low-Tension  Positively  Driven  Make-and-Break  Magnetos 
for  Stationary  Engines 

of  the  engine.  The  shut-off  switch  can  be  put  in  series 
with  the  wire  leading  to  the  igniter,  or  it  can  be 
arranged  to  ground  the  magneto  by  short  circuiting 
the  armature,  thereby  cutting  off  ignition. 

RELATION   OF  ENGINE  AND  MAGNETO   SPEEDS. 

It  is  not  necessary  to  use  every  current  wave 
that  is  produced.  A  four-cycle  single  cylinder  engine 
calls  for  one  spark  every  other  revolution  of  the  crank 
shaft;  therefore,  if  the  magneto  is  run  at  engine  speed, 
only  one  out  of  every  four  current  waves  will  be  used. 
A  single  cylinder  two  cycle,  and  a  two  cylinder  four 
cycle  engine  will  use  every  other  wave ;  a  four  cylin- 
der, four  cycle  engine,  which  requires  two  sparks 
every  revolution,  will  use  every  impulse.  It  is  often 
necessary  with  low  speed  engines  to  run  the  mag- 
neto twice  engine  speed  in  order  to  increase  its  effi- 
ciency and  make  starting  on  the  magneto  easier.  This, 
of  course,  doubles  the  number  of  current  waves,  which 
is  immaterial,  but  also  reduces  by  one-half  the  avail- 
able spark  advance.  A  magneto  giving  a  current  wave 
strong  enough  to  ignite  the  charge  during  60  degrees 
of  armature  revolution,  will  allow  the  same  number 
of  degrees  spark  advance  on  the  crank  shaft  if  run  at 
engine  speed,  and  only  half  as  much  or  30  degrees  if 
driven  twice  engine  speed. 

MULTIPLE  CYLINDER  ENGINES. 

This  type  of  magneto  will  give  good  results  on 
engines  of  more  than  one  cylinder  provided  it  is  cor- 
rectly timed.  The  igniters  on  the  different  cylin- 

127 


Ignition 

ders  are  all  connected  to  a  common  wire  leading  to 
the  collecting  brush  on  the  magneto.  The  two  princi- 
pal things  to  observe  are:  First,  the  magneto  must 
be  driven  at  such  a  speed  that  a  current  wave  will  be 
at  its  maximum  every  time  any  of  the  igniter  points 
separate;  second,  the  igniters  must  be  so  arranged 
that  at  the  instant  any  one  of  them  snaps — causing 
ignition — all  the  others  will  be  out  of  contact.  It  is 
easy  to  see  that  if  any  of  the  other  igniters  are  in 
contact  when  ignition  is  required  in  cylinder  No.  1,  the 
current  will  flow  across  them  rather  than  produce  an 
arc  in  the  first  cylinder. 

It  is  often  a  good  plan  with  single  cylinder  engines 
to  run  the  magneto  at  1%  engine  speed.  This  makes 
use  of  some  positive  and  some  negative  waves,  caus- 
ing the  current  to  reverse  its  direction  across  the 
igniter  points  every  time  they  separate.  Under  these 
conditions  "pitting"  of  one  point  and  "building  up" 
on  the  other  is  impossible  and  the  wear  is  uniform. 

WEAR  OF  IGNITER  POINTS. 

The  igniter  points  will  last  considerably  longer 
with  this  type  of  magneto  than  with  battery  sys- 
tems. This  is  due,  in  part,  to  the  fact  that  much 
less  amperage  passes  across  the  arc  when  a  magneto 
is  used  than  with  a  battery  and  coil.  The  oscillograms 
on  page  45  show  that  with  battery  systems  from  1  to 
4  amperes  pass  through  the  arc,  while  the  maximum 
current  possible  with  the  magneto  giving  the  current 
wave  shown  on  page  124  is  0.25  of  an  ampere.  The 
several  different  makes  of  magnetos,  however,  differ 
somewhat  in  this  respect.  Some  machines  having 

128 


Low-Tension  Positively  Driven  Make-and-Break  Magnetos 
for  Stationary  Engines 

armatures  of  less  resistance  give  twice  as  much  am- 
perage, but  even  then  the  wear  on  the  igniter  points 
is  very  slight. 

INSULATION  OF  IGNITER. 

The  successful  operation  of  the  magneto  depends 
to  a  large  extent  upon  the  insulation  of  the  stationary 
igniter  point.  Two  or  three  times  the  insulation  ordi- 
narily used  is  necessary,  particularly  since  a  lack  of 
sufficient  insulation  at  this  point  is  so  common  a  fault 
with  battery  systems.  The  reason  for  this  is  simple : 
The  voltage  of  the  magneto  is  several  times  that  of 
a  set  of  4  or  6  dry  cells,  and  so  if  a  greasy  carbon 
deposit  collects  on  the  surface  of  the  insulation,  which 
usually  happens  sooner  or  later,  the  higher  voltage 
of  the  magneto  finds  an  easy  path  across  it  to  ground. 
The  lower  curve  on  page  124  shows  that  the  open  circuit 
E.  M.  F.  rises  to  about  ISO  volts.  Since  several  of 
these  voltage  impulses  occur  between  successive  igni- 
tions when  the  igniter  points  are  separated,  the  insula- 
tion is  subjected  to  a  strain  of  150  volts  as  against 
about  6  volts  with  battery  systems.  If  mica  washers 
are  used,  they  should  be  extra  large  and  not  less  than 
J4  or  %  of  an  inch  thick.  The  voltage  will  not  punc- 
ture the  mica  but  will  "skate"  or  slide  a  considerable 
distance  over  the  surface,  particularly  if  it  is  blackened 
with  even  a  slight  carbon  deposit;  therefore,  the  "dis- 
tance to  ground"  must  be  kept  comparatively  great. 

Built  up  thick  mica  washers  are  not  entirely  sat- 
isfactory. They  are  quite  sure  to  loosen  in  time  and 
the  heat  and  pressure  of  constant  explosions  will  drive 

129 


130 


131 


Ignition 

grease  and  carbon  in  between  them.  A  form  of  mold- 
ed composition  or  so-called  "lava"  bushings  are  very 
good.  If  the  bushings  are  thoroughly  annealed,  to 
make  them  less  sensitive  to  sudden  changes  of  tem- 
perature, and  are  correctly  shaped  and  installed,  they 
will  be  very  durable  and  entirely  satisfactory.  A  cone- 
shaped  lava  bushing,  fitted  in  a  ground  taper  joint 
in  the  igniter  casting,  will  be  so  well  protected  me- 
chanically that  breakage  will  be  very  unlikely. 

When  kerosene  is  used  as  fuel,  the  problem  of 
insulation  is  more  difficult.  Mica  washers  seem  to 
break  down  sooner  and  are  even  less  satisfactory  than 
with  gasoline. 

HEAT  OF  ARC. 

The  temperature  the  arc  attains  is  not  as  important 
as  its  duration,  viz. :  the  actual  time  it  lasts.  Almost 
any  kind  of  an  electric  spark  is  hot  enough  to  ignite 
the  charge,  but  often  fails  to  do  so  because  it  does 
not  last  long  enough.  A  piece  of  paper  can  be  passed 
through  a  flame  without  catching  fire,  provided  it  is 
done  quickly.  The  gas  in  the  cylinder  ignites  very 
quickly,  to  be  sure,  but  some  kinds  of  sparks  are  even 
quicker,  and  ignition  fails  on  that  account. 

The  arc  from  this  type  of  magneto  is  of  ample 
duration  to  ignite  the  most  .stubborn  mixture,  in  fact 
its  duration  is,  as  a  rule,  longer  than  that  of  bat- 
tery systems.  The  applied  voltage  is  higher,  the 
inductance  of  the  winding  is  greater,  and  the  arma- 
ture continues  to  generate  current  for  a  part  of  a  sec- 
ond after  the  igniter  points  separate,  all  of  which  tends 
to  prolong  the  arc. 

132 


Low-Tension  Positively  Driven  Make-and-Break  Magnetos 
for  Stationary  Engines 

SIZES  OF  MAGNETOS. 

Make-and-break  magnetos  of  this  type  are  made  in 
two  principal  sizes,  generally  known  as  "Two  Magnet*' 
and  "Three  Magnet."  The  larger  machine  is  a  trifle 
longer  than  the  smaller  and  has  one  more  magnet. 
This  extra  magnetic  strength  and  length  of  armature 
makes  the  three  -  magnet  machine  more  efficient  at  very 
slow  speeds.  A  good  two-magnet  magneto  will  give 
a  spark  strong  enough  to  start  the  engine  at  22  revo- 
lutions per  minute,  while  the  larger  machine  of  same 
make  will  give  as  good  a  spark  at  12  revolutions  per 
minute.  For  engines  up  to  6  or  8  H.  P.  that  can  be 
easily  turned  over,  the  two-magnet  magneto  is  satis- 
factory, but  for  starting  larger  engines  the  three-mag- 
net machine  should  be  used.  Where  starting  is  accom- 
plished with  a  battery  and  cheap  coil,  and  the  mag- 
neto run  not  less  than  500  revolutions  per  minute,  the 
two-magnet  machine  will  operate  successfully  on 
engines  of  30  or  more  horsepower. 

OSCILLATING  MAKE-AND-BREAK  MAGNETOS. 
There  are  a  few  special  forms  of  magnetos 
arranged  to  be  attached  directly  to  the  igniter  plate. 
The  armature  is  fastened  to  the  movable  igniter  point 
so  that  it  will  oscillate  across  the  magnetic  field.  Syn- 
chronism between  the  armature  and  igniter  is  absolute 
since  they  are  both  operated  by  the  same  tripping 
mechanism.  The  tendency  in  designing  this  type 
of  magneto,  so  far,  has  been  to  make  it  too  small  and 
the  magnetic  circuit  of  too  high  reluctance,  resulting 
in  a  lack  of  reserve  spark  strength  to  meet  adverse 

133 


Ignition 

conditions,  and  in  the  magnets  losing  their  strength 
after  being  in  service  a  few  months.  This  type  is  stili 
in  the  experimental  stage,  but  the  idea  of  making  the 
magneto  a  part  of  the  igniter  itself  is  correct,  and 
the  practical  difficulties  attending  its  achievement  will, 
without  doubt,  soon  be  overcome. 

Since  reliable  ignition  apparatus  can  be  had  today, 
which  was  not  so  a  few  years  ago,  the  far  greater 
part  of  present-day  ignition  trouble  is  due  to  no  other 
cause  than  the  tinkering  and  guessing  of  the  man  who 
DOESN'T  KNOW. 


134 


A 

ALTERNATING   CURRENT— 91,   93;    Magneto  91. 

AMMETER — 22,  24,  89;  substitute  for,  in  testing  dry  cells  23;  hot  wire 
65  (foot  note). 

AMPERE— definition  of  13. 

AMPERE    HOUR— definition   of    14. 

ARC — (see   spark). 

ARMATURE — 77,  78,  79,  80,  117;  "drum"  79,  80,  83;  winding  of,  for 
dynamos  85;  "H"  97,  100,  101,  116;  winding  of,  for  high  tension 
magneto  99,  110;  winding  of,  for  make-and-break  magneto  119, 
123,  125;  position  of,  when  spark  occurs  104;  position  of  relative 
to  current  strength  100,  101,  125;  short  circuiting  of,  to  cut  off 
ignition  127;  re-actance  in  123;  clearance  of  110,  119;  high  ten- 
sion 113;  for  make-and-break  magneto  116,  117;  acting  as  make 
and  break  coil  117;  strengthening  magnetism  in  117;  energy 
stored  in  117;  protecting  of  from  dirt,  etc.,  122. 

B 

BATTERIES — Ch.  1  ;  primary,  definition  of  5 ;  theory  of  6 ;  internal  re- 
sistance of  7 ;  polarization  of  6 ;  closed  and  open  circuit,  definition 
of  6;  E.  M.  F.  of  23,  27;  amperage  of  24,  27;  installing  of  25; 
connecting  of  26;  "local  action"  of  10. 

Dry — 9,    10;    E.    M.    F.    of    24;    amperage    of    24;    current    from    28;    ef- 
ficiency   tests     of    29;     internal     resistance     of    24;     life    of    28; 
polarization  of   9;    recuperation   of    10;    test   for   amperage   of   22, 
23;    "local   action"   of    10;    connecting   of    27,    28. 
Edison    Primary — 7,    8. 
Edison    Storage — 12. 
Gordon — 8. 

Secondary    or    Storage — definition    of    5;    theory    of    11,    12;    care    of    25, 

26;    testing   of   24;    "floating  on   the   line"    87;    sulphation   of  25. 

BEARING — passing    current    through     119;    for    make    and     break    magneto 

122;    ball    115. 

BRUSHES — Collecting  78,  93;  carbon  85;  copper  plated  carbon  85,  122; 
for  dynamo  85  ;  copper  gauze  85 ;  trouble  with  86 ;  graphite  satur- 
ated 85,  122;  for  high  tension  magneto  110,  113,  116;  grounding 
119;  for  make  and  break  magneto  119,  121,  122;  sparking  and 
wear  of  121,  122;  contact  with  its  holder  85,  122. 
BUSHING— lava  132. 

C 

CAPACITY — electrostatic,    of    secondary    winding   63 ;    of    condensers    60. 
CARBON— for  brushes   85;    rod  for   dry   cell   5,   9,    27;    granular   for   dry   cell 

9 ;   resistance   of  21  ;   loose  contact   with    27. 
CELLS — (see    Batteries);    connected   in   series   27;    in    multiple    28;    in    series 

multiple  29. 

COBALT — as   a  conductor  of  magnetism   71. 
COIL — make-and-break    32.     36,    38,    42;    oscillograms    of    44    to    47;    E.    M. 

F.    of   spark   from   47. 

Jump    Spark — theory   of    51,    52,    54;    construction   of   Ch.    8;    oscillograph 
tests    of    Ch.    9;    E.    M.    F.    of    51;    producing    sparks    five    feet 
long   20. 
Non    Vibrating — 6'9. 

COLLECTING   BRUSHES— (See    Brushes.) 

COLLECTING    RING — for   high   tension    magneto    108.    110,    113;    for   A.    C. 

magneto    93;    for    make-and-break    magnetos    116,    119.    121,    122. 
COMMUTATOR— 54,    78;    construction    of,    for    dynamos    85;    burning    and 

roughening    of   86. 
COMPASS— 73,   75. 
COMPRESSION— loss    of   39. 


CONDENSER — 2,    52,    53 ;    construction    of    for    coils    59 ;    capacity    of    60 ; 

if  too   large   or  small   63;    for    high   tension    magneto    99,    110,    113.. 
CONDUCTANCE— definition    of    18. 

CONDUCTORS — definition   of   1;    best   known    14;    table   of   21. 
CONTACT — poor  on   dry  cells   27;    time   length   of   42,   46,   47,    70. 

Points. — Theory  of  wear  and  burning  of  39,  40 ;  for  igniter  40  ;  wear  of 
igniter  41,  48,  123,  125,  128;  adjustment  of,  for  make-and- 
break  magneto  127,  128;  adjustment  of,  for  high  tension  mag- 
neto 113;  for  vibrating  coils  53,  54,  58,  63;  adjustment  of  for 
vibrating  coils  58,  59. 
CORE-IRON — 36,  51;  importance  of  32,  47;  construction  of  56;  for 

armature   79. 

COULOMB — definition   of   14. 

COUPLING — for  driving  magnetos  105;  Oldham  104,  105. 
CURRENT — 1;  alternating  91,  93;  wave  in  magneto  95,  100,  124;  in 
primary  of  vibrating  coils  52,  54,  65,  66,  67,  69;  in  secondary  of 
vibrating  coils  52,  55,  60 ;  in  make-and-break  coils  45,  46,  47 ; 
current  producing  magnetism  31,  32,  33,  71;  momentum  of  33,  34; 
inertia  of  33,  34;  Foucault  or  Eddy  56,  79. 

D 

DISRUPTIVE    DISCHARGE— definition    of    19. 

DISTRIBUTOR— for  high   tension  magneto  96',   97,   111,   113;   care   of   108. 

DRY    CELL — 9,    10;    (see    Batteries). 

DUAL   SYSTEM— 97,   103,    111. 

DYNAMIC    ELECTRICITY— definition    of   3,    71,    Ch.    10. 

DYNAMO — 80,  81,  82;  shunt  wound  80,  81;  series  wound  81;  making  it 
"pick  up"  81;  variation  of  voltage  in  82;  construction  of  low 
tension  83  to  89 ;  regulating  voltage  of  86,  87,  89 ;  governor  for 
86,  89. 

DYNE^-74. 

E 

EDDY  OR  FOUCAULT  CURRENTS— 56,  79. 

ELECTRICITY— 1,  2,  3; 

Current-definition  of   1  ;    (see  current). 
Dynamic-definition  of   3,    71,    Ch.    10. 
Galvanic-definition    of    3. 
Static-definition   of   1,   2,    14,    53. 

ELECTROMOTIVE  FORCE— (E.  M.  F.)  definition  of  2;  unit  of  13;  of 
cells  23,  27 ;  production  of  by  magnetism  75  ;  variation  of  in  mag- 
neto 91,  95;  required  to  start  an  arc  50,  97,  99;  produced  in 
armature  97,  99;  produced  in  secondary  winding  51,  60,  99. 

ELECTROLYSIS— 119. 

ELECTROLYTE — definition  of  6;  for  dry. cells  9;  for  Gordon  and  Edison 
primary  cells  7;  for  secondary  or  storage  batteries  11,  87,  89;  for 
Edison  storage  battery  12. 

E.    M.    F.' — (see    Electromotive    Force). 

ETHER   OF    SPACED- 33. 

F 

FIELD — (see    Magnetic    Field). 

"FLOATING   BATTERY    ON   LINE"— 87,    89. 

FLUX — magnetic    75. 

FOUCAULT  OR  EDDY  CURRENTS— 56,  79. 

G 

GALVANIC    ELECTRICITY— 3. 
GALVONOMETER— 75. 


GAUSS — definition   of   75. 
GENERATOR — electric,    principle    of    75. 
GOVERNOR— for   dynamos   86,    89. 

H 

"H"   ARMATURE— 97,   100,    101,    116. 
HEAT — produced   by   current  in   wire   14;    of   spark   or   arc    50,   132. 

I 

IGNITER — 34,    37,   38;    points   for   40;    wear   of  41,    48;    insulation   of    129. 

IGNITION — make-and-break    30,    48;    jump    spark    49. 

INDUCTION — coil,   producing  spark  five   feet   long,   20. 

INDUCTOR — of   alternating    current   magneto   92,    93 ;    type  magneto    93,    95. 

INERTIA— (electric)    33. 

INSULATORS — definition   of    1;    table    of   21. 

INTERNAL    RESISTANCE— of  batteries    7,    24,    27,    28,    29. 

INTERRUPTER— ^for   vibrating    coils    53,    54,    56',    57,    58;    for   non-vibrating 

coils    68,    69;    for   high    tension    magneto    96,    101,    111,    113. 
IRIDIUM— 40,    58. 
IRON — as   a  conductor   of  magnetism   71  ;    for    core    (see    Core). 

J 
JUMP   SPARK— 49;    (see  Spark). 

K 

KEROSENE— as   fuel    132. 

L 

"LAG" — in    coils    67,    69;    magnetic    103. 
LAVA   BUSHING— 132. 
LINES    OF    FORCE — definition   of   71,    73,    74;    unit   of    74;    forming   around 

a   coil   32;    around   a   wire    carrying    a   current    31;    producing    E.    M. 

F.    by    "cutting''    51,    75,    76,    77. 
"LOCAL    ACTION"— in    galvanic    cells    10. 
LODGE — Sir    Oliver — 33    (foot    note.) 

M 
MAGNETIC— CIRCUIT— definition    of    73;    reluctance    of    79,    117,    133;    for 

high   tension    magneto   108,    109. 

Field — definition  of  73;  surrounding  wire  carrying  a  current  31.  33; 
34 ;  between  poles  of  a  magnet  74,  75 ;  increasing  strength 
of  79. 

Density — definition  of  75  ;   increasing   by   use  of  iron  core   32,   33. 
Lines   of    Force — see    "Lines   of   Force". 
Strength — 74. 
Plug   System — 48. 

MAGNETISM — 71,  75;  around  wire  carrying  a  current  31,  32,  33;  insu- 
later  of  71  ;  circuit  of  (see  Magnetic  Circuit)  ;  conductor  of  71  ; 
unit  quantity  of  74 ;  density  of  (see  Magnetic  Density)  ;  strength 
of  74 ;  producing  electric  current  from  75 ;  residual  81  ;  strengthen- 
ing of,  in  armature  99,  117. 

MAGNETO — definition  of  80;  variation  of  voltage  in  82,  91;  direct  cur- 
rent 89,  91  ;  alternating  current  91  ;  inductor  type  93,  95 ;  varia- 
tion of  voltage  in  inductor  type  95 ;  theory  of  high  tension  96',  97, 
99,  Ch.  12;  timing  of  high  tension  106,  107;  timing  of  make-and- 
break  125,  127.  128;  dual  type  97,  108,  114;  connecting  of  107; 
diagram  of  high  tension  109;  oiling  of  high  tension  115;  for  make- 
and-break  engines  116.  Ch.  14;  sizes  of  make-and-break  113; 
oscillating  types  133,  134;  interrupter  or  timer  for  high  tension  111. 


MAKE-AND-BREAK    IGNITION— 30,   48. 

MAXWELL— 74,    75;    J.    Clerk,   74. 

MICA — as    an    insulator    21 ;     for    insulating    commutator     85 ;     washers     for 

insulating    igniter    38,    39,    129,    132;    for    condenser    of    high    tension 

magneto    110. 
MICROFARAD— 60. 

MOMENTUM— of   electric    current   33,    41. 
MULTIPLE    CONNECTIONS— 17;    joint    resistance    of    17,    18;    current    in 

branch  circuits   of   18. 

N 

NICKEL — resistance  of  21;  as  a  conductor  of  magnetism  71;  for  igniter 
points  40. 

O 

OHM— definition    of    14,    15. 

OHM'S    LAW— definition   of    15,    16;    mentioned   46. 

OLDHAM-COUPLING— 104,    105. 

OSCILLOGRAPH— 43,    44;    diagram    of   46. 

OSCILLOGRAMS — of  make-and-break  coils  45;  of  vibrator  coils  66,  67; 
of  current  waves  of  inductor  type  magnetos  95 ;  of  current  in  "H" 
armature  100;  of  current  passing  through  arc  102;  of  current 
waves  in  make-and-break  magneto  124;  of  E.  M.  F.  waves  in 
make-and-break  magneto  124. 

P 

"PANCAKE    WINDINGS"— for    jump   spark    coils    61,    63. 

PARALLEL    CONNECTIONS— (see    Multiple    Connections). 

"PITTING" — of   contact    points,    theory    of    39,    40,    48,    58,    63,    113, 

PLATINUM— 40,    58. 

PLUG— spark,    51,    62. 

Magnetic,    system    48. 

POINTS — contact    (see    Contact    Points). 

POLARIZATION — explained  6;  .prevention  of  in  Gordon  and  Edison 
primary  cells  7;  prevention  of  in  dry  cells  9,  10;  effects  of  in 
dry  cells  9. 

POLE  PIECES— -79;  for  dynamo  83;  for  inductor  type  magneto  93;  for 
high  tension  magneto  109;  for  make-and-break  magneto  117. 

POWER — unit    of   electrical    15;    loss    of    in    gas    engine    39,    94. 

PRIMARY — of  jump  spark  coil  51,  56;  of  armature  of  high  tension  mag- 
neto 99. 

R 

RELUCTANCE — definition   of    73 ;    of   magnetic    circuit    79. 

RESISTANCE — unit  of  14;  of  different  materials  (table  of)  21;  of  arc 
or  spark  49;  of  spark  gap  52,  55;  internal  of  batteries  7,  24,  27, 
28,  29;  of  circuits  in  multiple  17,  18;  of  circuits  in  series  16';  of 
gases  50 ;  of  secondary  winding  52 ;  of  carbon  brushes  85. 

S 

SAFETY  SPARK  GAP — for  high  tension  magneto  107,  108,  109,  111,  113; 
causing  missing  explosions  111. 

SECONDARY— theory  of  51;  illustration  of  61;  winding  of  53,  60;  cur- 
rent in  52;  E,  M.  F.  in  51,  53,  54,  6'0 ;  insulation  of  60-63; 
number  of  turns  in  63;  "pancake"  winding  61-63;  of  high  tension 
magneto  armature  99. 

SELF-INDUCTION— of    secondary   winding    63. 

SERIES   CONNECTIONS— 16;    total    resistance    of    17;    of    cells    27. 


SHELF — or  base   on   which   to   mount   magneto    106,    125. 

SPARK — Jump — 49;  E.  M.  F.  of  49,  50,  51;  duration  of  55;  current  pass- 
ing through  102,  103;  heat  of  50;  resistance  of  49,  52;  tests  of 
in  air  51  ;  preventing  spark  at  contacts  52,  53 ;  shortening  of  63, 
64;  number  of  during  one  contact  of  timer,  65,  66,  67;  timing  of 
in  high  tension  magneto  104 ;  shutting  off  of  in  high  tension  mag- 
neto 107;  maintaining  of  in  high  tension  magneto  99,  101.  103; 
strength  of  in  high  tension  magneto  101,  103;  playing  around  glass 
plate  72. 

Make-and-Break — theory  of  33,  34;  E,  M.  F.  of  47;  duration  of  41, 
125,  132;  current  passing  through  45.  46,  128;  heat  of  132; 
resistance  of  49 ;  preventing  of  at  contacts  52,  53 ;  at  low 
speed  of  make-and-break  magneto  133;  advance  and  retard 
of,  in  make-and-break  magneto  123,  127;  timing  of,  in  make- 
and-break  magneto  125,  127,  128;  occurring  on  breaking  a 
circuit  34. 

Safety    Gap    (see   Safety   Spark    Gap). 
Plug— 51,    62. 
SULPHATION — of    storage    battery,    cause    and   remedy   for   25. 

T 
TABLE — of    comparative    resistance    of    materials    21  ;    of    life    of    dry    cells 

29;    of   driving   speeds    for   high    tension   magneto    104. 
TIME    LENGTH    OF    CONTACT— 70;    in    make-and-break    battery    system 

41,    42,    46,    47. 
TIMER — for    vibrating    coils,    54,    62;     for    non-vibrating    coils,    68,    6*9,    70; 

working    with     alternating     current    magneto    94 ;     for    high    tension 

magneto    96,    111,    113. 
TIMING — of    high    tension    magneto    106,    107:    of    make-and  break    magneto 

125,    127,    128;    of  igniter  41. 
TRANSFORMER— 96,    103,    108,    114. 

V 
VACUUM    IMPREGNATING   PROCESS— 60,    61. 

VIBRATOR — theory  of  53;  construction  of  56,  57,  58;  illustrations  of 
57;  "hammer  break'  58;  "freezing"  of  58;  current  required  to 
operate  65,  66,  67 ;  substitute  for  69 ;  working  with  alternating 
current  magneto  94 ;  adjusting  of  59. 

VOLT — definition    of    13. 

VOLTAGE — (see    Electromotive    Force). 

VOLTMETER— 24,    89;    electrostatic    47. 

W 

WASHERS — mica,    for    insulating    igniter    38,    39,    129,    132. 
WATT— definition   of   15. 
WAVES — current,    in    alternating    current    magnetos    93 ;    "sine"    94 ;    number 

of,     in     inductor     type     magneto     93 ;     oscillograph     records     of     (see 

"Oscillograms"). 
WIRE — heat    produced    in.    by   current    14;    size    of    for    connecting    coils    66; 

iron    for    core    56;    size    of    for    winding    make-and-break    coils     36; 

size    of   for  winding   primary    56;    size   of   for   winding   secondary   63; 

size   of  for   winding   high    tension    magneto    armature    99. 


14  DAY  USE 

RETURN  TO  DESK  FROM  WHICH  BORROWED 
LOAN  DEPT. 

This  book  is  due  on  the  last  date  stamped  below,  or 

on  the  date  to  which  renewed. 
Renewed  books  are  subject  to  immediate  recall. 


?*8tf 

R^C'D  CO 

!  A  M       4    1Q^R 

JHIM      4    «w" 

. 

General  Library 
LD  21A~50w-8,'57                                 University  of  California 
(C8481slO)476B                                                Berkeley 

YB  52023 


46451^ 


UNIVERSITY  OF  CALIFORNIA  LIBRARY 


